Visual acuity, the ability to see fine detail, is critical for many tasks. However, visual acuity is less than perfect in many people because of the curvature of the cornea and the length of their eye do not match. This is usually corrected with glasses, contact lens, or by surgically re-shaping the cornea (such as Lasik).

Reinhart, Xiao, McClenahan and Woodman (in press) improved visual acuity in a novel manner -- by applying direct current electrical stimulation to the visual cortex for 20 minutes (no -- it didn't hurt). Then they measured vernier acuity (the ability to line two lines up so they are collinear) of the parafoveal belt (the area in a ring around the fovea) and found that acuity was about 15% better than it was at baseline. The people with the poorest baseline visual acuity improved the most. When they reversed the orientation of the electric field, visual acuity was impaired.

I don't recommend that you try this at home.

Reinhart, R. M. G, Xiao, W., McClenahan, L. J., & Woodman, G. F. (in press). Electrical stimulation of visual cortex can immediately improve spatial vision. Current Biology. http://dx.doi.org/10.1016/j.cub.2016.05.019

Did you know that chocolate smells pink and stripy? How can something smell pink? Or, stripy? Welcome to the weird world of synesthesia which comes from the Greek words for "together" and "sensation". When a synthesthete experiences a stimulus in one sensory modality (such as vision) he or she also experiences the stimulus in another cognitive or sensory pathway.

Synesthesia comes in many different forms. One of the most common is grapheme-color synesthesia in which a letter or number (a grapheme) printed in black ink is perceived in a particular color. While there are individual differences in the color that a given grapheme might be perceived, it is common for the letter "A" to be perceived as red.

About 4.4% of synthesthetes experience odor-color synthesthesia -- when they smell an odorant, they also experience a vision. Rusell, Stevenson and Rich (2015) studied six odor-color synthesthetes by presenting an odorant either nasally (orthonasally) or through the mouth (retronasally). Retronasal presentations of odorants are often perceived as a flavor rather than an odor. This allowed Rusell et al. to explore whether awareness of sensory modality influences synthesthesia or not.

The use of odorants also allowed Russell et al. (2015) to contrast two classes of theories of how synthesthesia arised. This is based on the fact that odorants are often difficult to correctly identify when they are presented in isolation. One class of theories claims that synthesthesia relies on low level perceptual mechanisms. If this class of theories is correct, the experience of synthesthesia should be the same whether the odor is identified or not. Another class of theories claims that synthesthesia involves higher order cognitive processes. This class of theories can more easily explain a difference between the experience of synthesthesia with identified vs unidentified odorants -- identifying the odor is a higher order process.

The synthesthetes experienced the odorant (ortho- or retronasally), attempted to identify it, and then drew their visual experience of the odorant. Being able to identify the odorant was critical for having a consistent visual experience with the odorant. This supports a more cognitive explanation of how synthesthesia arises.

Even though the article is called "Chocolate smells pink and stripy", Russell et al. (2015) did not use chocolate as an odorant. The words "chocolate", "pink", and "stripy" only appear in the title! So, I am not sure that chocolare smells pink and stripy even to an odor-color synthesthete.

Russell, A., Stevenson, R. J., & Rich, A. N. (2015). Chocolate smells pink and stripy: Exploring olfactory-visual synesthesia. Cognitive Neuroscience, 6, 77-88. http://dx.doi.org/10.1080/17588928.2015.1035245

Eklund, Nichols and Knutsson (2016) claim that the statistical methods used in fMRI studies have never been validated with real data. When they did so, they found false- positive rates (Type I errors) of up to 70% -- more than a wee bit above the α level of 5% that is typical in most psychological studies. That is, the results of many fMRI studies that you hear about in class or read about, may be wrong.

Eklund, A., Nichols, T. E., & Knutsson, H. (2016). Cluster failure: Why fMRI inferences for spatial extent have inflated false-positive rates. Proceedings of the National Academy of Sciences of the United States of America, early edition. http://dx.doi.org/10.1073/pnas.1602413113

My two picks for the best illusion of the year placed second and first! If you haven't looked at the illusions yet, what are you waiting for?

Crichton, Elias ∧ Alkerwi (2016) used data from the Maine-Syracuse Longitudinal Study to look at the relation between chocolate consumption and cognitive functioning while (statistically) controlling for cardiovascular, lifestyle and dietary factors. Habitual chocolate consumption predicted several measures of cognitive performance -- visual-spatial memory, working memory, abstract reasoning, and everyone's favorite -- the Mini-Mental State Examination. Those who reported eating more chocolate had better cognitive functioning than those who reported eating less chocolate. What are you waiting for? GO EAT SOME CHOCOLATE!

Remember that correlation does not imply causation...

Crichton, G. E., Elias, M. F., & Alkerwi, A. (2016). Chocolate intake is associated with better cognitive function: The Maine-Syracuse longitudinal study. Appetite, 100, 126-132. http://dx.doi.org/10.1016/j.appet.2016.02.010

There are some really interesting ilusions (not just visual!) at Illusion of the Year. You can vote for your favorite until 4 PM EDT today, June 30.

My favorites this year are The Ambiguous Cylinder Illusion and Motion Integration Unleased: New Tricks for an Old Dog.

Be sure to scroll down on the home page and look at some of the top rated illusions.

Messerli (2012) cites research that found that flavanols, which are found in cocoa, green tea and wine, seems to slow down, and, in some cases, reverse cognitive deficits that occur as we age. So, if we want to be smarter, should we be eating lots and lots of chocolate?

Messerli (2012) looked at the relation between the amount of chocolate consumed and the number of Nobel laureates. He wanted to know if countries where people ate more chocolate, on average, produced more Nobel laureates than countries where people ate less chocolate on average. His findings indicate a strong linear relation (r = .79) between the amount of chocolate consumed per capita in countries and the number of Nobel laureates per 10,000,000 people in those countries. According to the regression equation, if everyone in a country increased the amount of chocolate eaten by about 0.4 kg (0.9 lb) per year, then the country would produce an additional Nobel laureate.

Yeah, I know that those results are correlational and that correlation does not imply causation (and so does Messerli). But I don't need much of an excuse to want to eat more chocolate.

Messerli, F. (2012). Chocolate consumption, cognitive function, and Nobel laureates. The New England Journal of Medicine, 367, 1562-1564. http://dx.doi.org/10.1056/NEJMon1211064

Do the two oblique lines appear to be collinear (falling on the same line)? Most people perceive the oblique line on the right as higher than it would be if it was collinear with the line on the left. Get a straight edge (a piece of paper will do) and lay the edge of the paper right on the oblique line on the left hand side of the illusion. Yup, the edge of the paper is also right on the oblique line on the right hand side of the illusion -- the two line segments are collinear.

This illusion is named after Johann Christian Poggendorff who was the first to notice (and report) the illusion. To find out about why the Poggendorff illusion is believed to occur and to try your luck in getting the two oblique lines to be collinear, visit and read this page.

Wilhelm Wundt introduced the horizontal - vertical illusion to the world in 1858. In the above figure, which looks longer -- the horizontal line or the vertical line? Having been exposed to many illusions in Perception, you already know that the lines are the same length, but to most people the vertical line looks longer than the horizontal. You can try adjusting the length of the vertical line to match the length of the horizontal line here.

There are several theories about why the horizontal-vertical illusion arises. One claims that we misapply depth cues -- the vertical line appears to recede into the distance. If the perception of size is proportional to the product of the visual angle of the object and the perceived distance, then the vertical line should appear longer than the horizontal line if the vertical line appears, at least partially, farther away. A second says that we judge line length based on the amount of effort it takes to move the eyes while looking at the lines. Because English is read left to right, it should take a little less effort to us English speaking people to move our eyes across the horizontal line (all that reading builds up the lateral and medial rectus muscles) than to move them across the vertical line (the inferior and superior rectus muscles are relative weaklings). Thus, the vertical line appears longer. Another theory says that the illusion is a framing error. Because the eyes are to the right and left of each other, we have a larger horizontal field of view than our vertical field of view. The vertical line fills up more of the frame's (field of view's) vertical space than the horizontal fills the frame's horizontal space. Because the vertical line fills more of the frame than the horizontal line, the vertical line must be longer.

You have probably seen ads for ways of improving your cognitive abilities through a training program. Research tends to indicate that, yes, you can improve your IQ by three to four points through cognitive training. Three or four points may not sound like a lot, but it is a substantial and noticeable improvement when talking about IQs.

New research by Foroughi, Monfort, Paczynski, McKnight and Greenwood (2016) question the results of those studies. Foroughi et al. thought that the effects seen in the previous research might be due to a placebo effect and a non-representative sample. That is, they hypothesized that participant recruitment materials advertising expected benefits of cognitive training might have lead to a self-selected, biased sample of individual who expect such an improvement, and that such expectations are the cause of the observed increase in cognitive ability. Most studies in this area use such overt participant recruitment materials according to Foroughi et al.

Foroughi et al. (2016) recruited participants with two flyers -- an overt flyer that explicitly mentions brain training, cognitive enhancement and that numerous studies have found a benefit of such training and a control flyer that requested participants to be in a study. Both groups took intelligence tests before cognitive training, had one hour of cognitive training, and then took the intelligence tests again on the following day. All researchers interacting with the participants were blind as to the condition the participants were in. Thus, the only difference between the two groups was the flyer that they saw and any expectations that the flyer induced.

There was no statistically reliable difference in how the two groups performed on the initial intelligence tests. Also, there was no statistically reliable difference in how the two groups did on the cognitive training. However, the overt group -- the group that should show a placebo effect -- showed an increase in intelligence of roughly 5 to 10 points after cognitive training but the control group -- the group with no placebo effect -- did not show a pre- to post-test difference in intelligence.

Because one hour of training is unlikely to produce such a large effect on intelligence, and it appears to do so only for the group expecting such an increase, and because the effect is comparable to the size of the effect seen in the literature, Foroughi et al. (2016) suggest that the effects seen in the literature may be at least partially due to participant's expectations and not to cognitive training per se. Foroughi et al. encourage future researchers in this area to control for such expectancy effects by using a double blind paradigm -- neither participants nor the researchers who interact with the participants should be aware of the purpose of the study. You might want to think twice before investing time, effort and money in a cognitive training program. You might want to at least wait until better evidence is found for their efficacy.

Foroughi, C. K., Monfort, S. S., Paczynski, M., McKnight, P. E., & Greenwood, P. M. (2016). Placebo effects in cognitive training. Proceedings of the National Academy of Sciences of the United States of America, Early Edition. http://dx.doi.org/10.1073/pnas.1601243113

Who is shown in the above picture? If you can't say, that is fine. Almost 98% of the information (in a non-technical sense) in the original picture has been removed -- each pixel in a 7 X 7 square has been replaced with the average brightness of those 49 pixels. This process is sometimes call pixelation. It is somewhat amazing that with so much of the information gone that you can still tell that it is a picture of an old man, even if you can't identify him.

You can make the picture more clear by squinting and/or backing away from it for a couple of meters. In place of squinting, poking a hole in a piece of paper with a straight pin and then looking through the hole is even better.

Pixelating the picture removes the high spatial frequencies from the picture -- the lines and edges that are important to form perception. Increasing the distance between you and the picture decreases the visual angle of the picture which implies that the spatial frequencies in the picture increase. As pupil size decreases, spherical and chromatic aberrations decrease which effectively make the visual image less blurry (or more sharp -- that is, the higher spatial frequencies are present).

You can upload and make your own pixelated pictures (with various amounts of pixelation) by visiting this page. That page also has a more detailed explanation of the effect.

By the way, the man in the picture is Gustav Theodor Fechner, the founder of psychophysics.

In this exciting video, Drogon fights the invisible menace. Will he save all of feline-kind? Will the tuna be saved from the evil fiends of the Dog Star (Sirius)? You will have to adopt him to find out the answer to these and other monumental questions. Drogon is available for adoption at the Humane Society of Greater Dayton.

OK -- I goofed. That is actually Annie who is Drogon's sister. It just doesn't sound as interesting to say Annie vs the Invisible Menace. Both Annie and Drogon are still available. Drogon is solid black and didn't have the cute paw action that his sister has. Adopt both!

Drogon's beautiful white mystacial vibrissae (whiskers) carry tactile information to sensory receptors in the follicle. The tactile information is sent to the barrel cortex which allows him to create a three dimensional map of his surroundings (so even if the invisibile menace from the Dog Star can't be seen, they might be sensed by the vibrissae). The vibrissae help cats sense whether they can fit through a hole and are used to help sense captured prey that are so close to the cat's mouth that they are out of visual range.

The above image is called Ehrenstein's Square Illusion. Yes, the thing that looks like a diamond with its sides bowed into toward the center is actually a square. Get a straight edge (a piece of paper works well) and lay it along one of the edges to see that the edges are in fact a straight line and not curved.

Ehrenstein was a Gestalt psychologist who initially published his illusion in 1925 (in German). Since I can't read German, I don't know what his explanation was. But based on other things written about his work, I am guessing that Ehrenstein would argue for top-down processing (which includes the effects of the context -- the surrounding circles) and prägnanz -- the simplest plausible explanation of a visual scene will be the one chosen by the visual system. In the presence of lots and lots of curves, the physically straight lines are probably curved too. If you have a better explanation, let me know (you can use my UD email address).

What do you predict would happen if you drew a perfect square on this background? Click on it to find out. This page lets you explore what happens to the illusion as you change the density of the background. What do you predict will happen to the illusory curvature of the square as the density of circles or arcs increases? Decreases?

Buried in all of those randomly oriented lines is a secret message. It is pretty hard to see (otherwise it wouldn't be quite so secret). Need some help? Click on the "See It" button and the secret message should be revealed.

Why is the "secret" message easier to see when it is moving? All of the elements of the message move together so they are grouped by the gestalt principle of common fate. Once they are grouped, it is much easier for the visual system to do form perception and for you to read the secret message.

Osteen et al. (2016) have identified a previously undiscovered source of nociception in mice. While studying venoms, they found two toxins from Heteroscodra maculate (a type of tarantula) that cause pain by activating ion channels (Na_V1.1) that where not thought to be involved in pain. While the toxin is chemical in nature, this source of pain is most associated with mechanical pain, such as pinching. There are a lot of this type of ion channels in the gut and it is suggested that these ion channels might play a role in irritable bowel syndrome (IBS). Besides helping us understand the physiological basis of pain, this discovery could lead to the development of a new class of drugs which might allieve the pain associated with IBS.

Osteen, J. D., Herzig, V., Gilchrist, J., Emrick, J. J., Zhang, C., Wang, X., Castro, J., Garcia-Caraballo, S., Grundy, L., Rychkov, G. Y., Weyer, A. D., Dekan, Z., Undheim, E. A. B., Alewood, P., Stucky, C. L., Brierley, S. M., Basbaum, A. I., Bosmans, F., King, F., & Julius, D. (2016). Selective spider toxins reveal a role for the Na_V1.1 channel in mechanical pain. Nature, online first, http://dx.doi.org/10.1038/nature17976

My office is on the third floor of St. Joseph Hall. So when I saw a man standing outside my office window, it was somewhat creepy even though I had been expecting it. St. Joseph Hall is getting a new roof this summer, and the roofing company has been encasing it with scaffolding. Yesterday they put the scaffolding up outside my office window.

I'm not sure that I would want to check my cell phone while standing on a two foot wide plank three stories in the air....

If you are like most people, when you look at the above drawing, you will see a turquoise circle in the center of the drawing. Only the arcs are turquoise -- the area between the turquoise arcs is really white. The color of the arcs has spread to fill the illusory contour that is perceived as an oval in the center.

Why does neon color spreading occur? No one has a definitive explanation. One explanation is that our visual system prefers the simplest, plausible description for a given visual scene (remember prägnanz from the gestalt movement? "Prägnanz" acutally means "pithiness" in German). One description is that there are four groups of four circles each. Each circle is drawn in two colors -- black and turquoise. In the top group, the circles are black in the upper 240 degrees of the circle and turquoise in the bottom 120 degrees of the circle. In left group, the circles are black in the left 240 degrees of the circle and turquoise in the right 120 degrees of the circle. And so on and so forth. That is quite wordy. A simpler descriptions is that there are four groups of four black circles each. Superimposed on top of the four groups is a transparent turquoise circle. That is simpler (or more pithy)! If prägnanz rules, we should see the center of the image as a transparent turquoise circle -- which means that the center of the image should appear turquoise. Since most people see it that way, prägnanz wins!

You can click on the image to go to a page where you can change the color of the turquoise arcs. If you play with it a bit, you will find that some colors work better than others for creating neon color spreading.

Orefice et al. (2016) studied developing mice with mutations in genes related to autism. When these mutations were limited to the peripheral nervous system, the mice showed abnormally large responses to puffs of air to the their skin and had problems distinguishing smooth and rough objects. There is some evidence that the brains of people with autism respond differently to light touches.

In some of the mice, these mutations not only changed the sense of touch but also lead to anxiety-like behaviors and less interaction with other mice.

Orefice, L. L., Zimmerman, A. L., Chirila, A. M., Sleboda, S. J., Head, J. P., & Ginty, D. D. (2016) Peripheral mechanosensory neuron dysfunction underlies tactile and behavioral deficits in mouse models of ASDs. Cell, 16, 1-15. http://dx.doi.org/10.1016/j.cell.2016.05.033 (the DOI wasn't working this morning -- the URL is http://www.cell.com/cell/fulltext/S0092-8674(16)30584-0)

Aperture size

How would you describe the blue object? Does it look like a pulsating plus sign? Or does it look like a plus sign that gets closer, then farther from you? It is neither. The object is seen through the aperture (gap) created by the tan rectangles.

Drag the slider next to "Aperture size" just a little tiny bit to the right to make the aperture just a bit bigger. When you can easily see the 90° corner passing through the aperture, your perception should change. If the blue object now looks like a rotating square that gets bigger (or closer) and then smaller (or farther away), you are closer to a veridical (truthful) perception but still not quite there.

Open the aperture as far as it will go (drag the slider all the way to the right) to see the true nature of the blue object. It is just a rotating square -- it isn't getting bigger (or closer) or smaller (or farther).

Now that you know that the blue object is just a rotating square, return the aperture to its smallest size. I get yet another perception -- a diamond getting bigger and smaller. I even get the subjective contours of the diamond and some bleed through of the blue diamond into the tan rectangles. That is, the corners of the tan rectangles near the blue object appear slightly darker and the darkened region grows and shrinks as the blue "diamond" appears to move closer and farther away.

We didn't have time to talk about motion perception in class last semester. So you missed out on the aperture problem. The aperture problem involves looking at a moving object through a small aperture -- a small slit or other shape. Apparent movement within the aperture often is quite different from the actual movement of the object. This page has an example of the aperture problem. When you first load the page, the grey edge appears to move from the lower right toward the upper left and vice versa. But the actual motion of the grey edge is quite different -- click on the "b Whole square" beneath the animation. The grey edge is actually moving straight up and down!

The aperture problem arises because local motion (the motion within the aperture) is ambiguous -- it can be interpreted in more than one way. Since the neurons which arise early in the visual system (e.g. retina, LGN, V1) deal with only local motion (that is, their receptive fields are relatively small), they cannot unambiguously identify the direction of motion and can suffer from the aperture problem. Using non-local information (such as the four edges option) or a corner (which is not ambiguous) helps us perceive the correct motion in many (but not all) cases. Later in the visual system (such as in area MT) the receptive fields can be quite large and thus those neurons do not suffer from the aperture problem.

Here is another example.

I hope that everyone had a great hug your cat day on Saturday (June 4). That is my daughter and Caroline from the Humane Society of Greater Dayton on hug your cat day. Caroline has diabetes and is in her new home by now.

So the rule is, if I show you a cute animal, I have to tell you something about its perception. Often people think that cats can see ghosts. Why else do they sometimes stare at a blank wall or ceiling very intently -- there is nothing there for us mere humans to see. While it isn't a ghost, cats can see things that humans cannot see. Campbell, Maffei and Piccolino (1973) studied the contrast sensitivity of Felis catus (the common domestic or feral cat) and found that cats can see lower spatial frequencies than humans. Remember that low spatial frequencies correspond to roughly uniform fields, like ghosts. So, when cats are staring at what we think is a blank wall, they might be seing something that we cannot see, but I doubt that it is a ghost.

So are cats always superior to us humans? If you asked them, they would probably say "yes -- and by asking such a stupid question you have demonstrated your inferiority." But when it comes to vision, humans are better at detecting higher spatial frequencies -- those lines and edges that make reading this possible. So when your cat looks at you on hug your human day, your image is probably a bit blurry to the kitty.

Campbell, F. W., Maffei, L. & Piccolino, M. (1973). The contrast sensitivity of the cat. The Journal of Physiology, 229, 719-731. http://dx.doi.org/10.1113/jphysiol.1973.sp010163

There has been a lot of research on the ability of dogs to communicate with humans (see the introduction of the article for a summary). But what about cats? The typical response of my cat Lancelot (that is him on the left) when I call his name is for him to ignore me. Does he not recognize my voice? Try it -- call "Lancelot". See, he didn't respond at all to you and that is exactly what he does to me.

Saito and Shinozuka (2013) tested 20 cats to see if they responded more to their human companion's voice than they do to a stranger's voice saying the same thing. Saito and Shinozuka recorded the voice of five people (four strangers and the cat's human companion) calling each cat's name. They then played these recordings to each cat and observed the response of the cats (ear movement, head movement, pupil dilation, vocalization, tail movement and movement of the cat) to each voice. Saito and Shinozuka conclude that cats do recognize their human companion's voice. Thus, I guess that Lancelot simply chooses to ignore me when I call him.

Saito, A., & Shinozuka, K. (2013). Vocal recognition of owners by domestic cats (Felis catus. Animal Cognition, 16, 685-690. http://dx.doi.org/10.1007/s10071-013-0620-4

Certain static images often lead people to see illusory motion. One of the more famous illusory motion examples is Kitaoke's rotating snake illusion (Ashida, Kuriki, Murakami, Hisakata & Kitaoka, 2012):

Image by Cmglee from Wikimedia commons (click image for information).

Anyone who has ever had a kitten knows that motion often triggers their hunting reflex. There are YouTube videos of cats attacking the rotating snakes illusion:

The video suggests that cats are sensing the illusory motion in the static image. But are they really doing so? Bááth, Seno and Kitaoka (2014) investigated this question by showing 11 cats in a cat-café (why can't we have a cat café in Dayton???) the rotating snakes illusion and a control image which does not induce illusory motion in humans. Unfortunately, the cats showed little interest in either image. They tried again with another clowder of cats (that is what a group of cats is called), but again, there was no hunting behavior. Thus, the question remains unanswered. If you have a cat, or especially a playful young kitten, give it a try! Here is the image that Bááth et al. used. The control image is also available.

Ashida, H., Kuriki, I., Murakami, I., Hisakata, R., & Kitaoka, A. (2012). Direction-specific fMRI adaptation reveals the visual cortical network underlying the "Rotating Snakes" illusion. NeuroImage, 61, 1143-1151. http://dx.doi.org/10.1016/j.neuroimage.2012.03.033

Bååth, R., Seno, T., & Kitaoka, A. (2014). Cats and illusory motion. Psychology, 5, 1131-1134. http://dx.doi.org/10.4236/psych.2014.59125

Why are bumblebees so fuzzy and what does it have to do with perception? Sutton, Clarke, Morley and Robert (2016) discovered that the hairs that makes bees fuzzy are actually mechanosensory receptors. Rather than responding to touch, the bumblebee's mechanosensory receptor hairs bend in response to electric fields. The bending, like the cilia of the inner hair cells in the cochlea, result in neurological events. That is, the bumblebee fuzz transduces electrical fields allowing the bee to sense electrical fields.

Why would bumblebees (like some species of shark) need to sense electric fields? The answer may be flower power. Flowers, like most living things, emit electrical fields that are strong enough to be sensed by the bumblebee fuzz. Sutton et al. did not investigate whether bumblebees use this sense to help them locate flowers, but it is would be an interesting question to investigate.

Sutton, G. P., Clarke, D., Morley, E., & Robert, D. (2016). Mechanosensory hairs in bumblebees (Bombus terrestris) detect weak electric fields. Proceedings of the National Academy of Sciences of the United States of America, Early Edition, 1-5. http://dx.doi.org/10.1073/pnas.1601624113

Artists often know quite a bit about perception even if they have never had a course in perception. Scientists who study perception sometimes use art either as their inspiration or in their research. This web page at Artsy looks at the relations between art and neuroscience. It includes several interesting examples of op art that demonstrate fundamental principles of perception.

I hope you have a great Memorial Day weekend. Take time to remember the true nature of the holiday and to honor those who have died serving in the armed forces.

Meet Mr. Noodles. He is one of my buddies at the Humane Society of Greater Dayton (he is still available at the time of writing; UPDATE: He has a forever home now!). He is watching the birds at the bird feeder outside the open cat room at the shelter. One look at Mr. Noodles' tail tells a tale of frustration toward the window that separates him from a tasty snack. How can we tell that his tail is switching (and therefore that he is frustrated) in a static photograph?

The motion cue here is motion blur. Motion blur occurs when an object moves too quickly relative to the time that the shutter is open on the camera (or the time to read the image data from the sensor in a camera). In such cases, the object (tail in this case) occupies several locations on the sensor and therefore looks like it is out of focus (it is blurry).

The same type of thing can happen on the retina but is usually less noticable unless the object is moving very quickly. When it does occur, especially when viewing static images, the visual system can use it as an indication of motion.

No, that is not Fred the Chicken! If you don't recognize the picture as me, then you really were asleep during class. What am I doing upside down? I'm trying to make a point about face perception. Please help me for a moment and turn me right side up by moving your mouse over my picture. That's bettter! Thanks!

But wait! When I am right side up, I look strange (or maybe more strange if you thought I was already that way upside down). What is going on? If you look at the right side up me, you will see that my mouth is actually upside down. That is (part of) what makes me look so strange. You probably did not notice that my mouth was right side up when the entire picture was upside down and I didn't look so strange when upside down.

This is called the face inversion effect or Thatcher illusion (named in honor of former British Prime Minister Margaret Thatcher, the Iron Lady, who appeared in the original illusion by Peter Thompson). The illusion is often used to study whether we perceive faces as a gestalt (as a single unit) or whether we perceive faces as a set of individual features. A quick Google search with "Thatcher Illusion" will give you lots of examples to laugh at. Many of the examples are better than the picture of me as they often invert the eyes as well as the mouth.

Most psychology students learn at least a little about the history of their discipline in their Intro course or a lot in a History course. While that history may stretch back to the ancient Greeks (or earlier depending on the textbook), most consider Wilhelm Wundt as the founder of the discipline's first official lab. A recent article by Schwarz and Pfister (2016) calls attention to a little known antecedant to Wundt's work -- Ferdinand Bernard Ueberwasswer.

Well before Wilhelm Wundt established the first psychological laboratory in 1879, and even before Fechner did his seminal work on psychophysics in the mid 1800s, there was Ferdinand Bernard Ueberwasser, who designated himself as a professor of psychology (Schwarz and Pfister, 2016). Records from the University of Münster indicate that in 1803, Ueberwasser was identifying himself as a professor of psychology and logic. Ueberwasser also wrote psychology textbooks including Anweisungen zum regelmäβigen Studium der Empirischen Psychologie für die Candidaten der Philosophie zu Münster (Instructions for the regular study of empirical psychology for candidates of philosophy at the University of Münster) which was published in 1787 (Schwarz & Pfister). This indicates that Ueberwasser viewed psychology as a science well before Wundt was even born (in 1832). (Yeah, "empirical" probably meant introspective in the title, but according to Schwarz and Pfister, Ueberwasser's textbook distinguished between introspection and scientific psychology and devoted several introductory chapters to the methodology of studying psychology scientifically.)

Schwarz, K. A., & Pfister, R. (2016). Scientific psychology in the 18^th century: A historical rediscovery. Perspectives on Psychological Science, 11, 399-407. http://dx.doi.org/10.1177/1745691616635601

No, that is not Fred the Chicken. It is a chicken I meet Sunday at Carriage Hill Metropark which is a living, 1880s farm in Dayton. If you like seeing farm animals (lots of sheep, some horses, cows, donkeys, chickens, pigs, a cat, a goat and a turkey) or like learning about how people lived in the 1880s, be sure to visit some weekend when you are back in Dayton.

Chickens have a couple of unusual features in their visual system. First, they are tetrachromatic -- they have four types of cones rather than three. The spectral sensitivity of the fourth type of cone is predominantly in the ultraviolet region. This allows them to see some types of bugs better and to also gauge the health of their chicks (growing chicken feathers reflect UV light).

Chickens have two fovea in each eye -- one that is used primarily for looking at distant objects and the other for looking at nearby objects. I have no answer to why they have two fovea, but I'm sure that it serves (or served) some evolutionary advantage to gallus gallus domesticus.

For laughs, search Wikipedia for "chicken eyeglasses".

What would you perceive if you looked at a cookie with a bite out of it? Would the perception be a cookie with a bite out of it, or would the bite be a cognitive interpretation of the perception of a weirdly shaped cookie?

Chen and Scholl (2016) investigated this question by showing participants a square which changed to a square with a piece missing from it (cookie, to a cookie with a bite out of it). The change could be sudden (directly changing from the square to the square with a piece missing) or gradual (changing from the square to a square with part of a piece missing to a square with the whole piece missing). The missing piece could either be plausible (a bite out of the cookie) or implausible (a hole which could not be made by taking a bite). Chen and Scholl asked people to rate whether the change was sudden or gradual.

When the change was plausible, the participants were much more likely to perceive the change as gradual even if the change was sudden compared to when the change was implausible. With a lot of control conditions, Chen and Scholl (2016) rule out the cognitive explanation -- the perception per se includes the causal history of the missing piece. We actually perceive the history of the cookie -- that someone took a bite out of it. Chen and Scholl conclude that "vision is richer and 'smarter' than it is often given credit for."

Chen, Y., & Scholl, B. J. (2016). The perception of history: Seeing causal history in static shapes induces ilusory motion perception. Psychological Science, 27, online before print. http://dx.doi.org/10.1177/0956797616628525

Science News has an article on how biologists are expanding their definition of "eye". Many critters have light sensing receptors (as defined by the presence of opsins -- the light-sensitive proteins found in photoreceptors such as rods and cones) but do not have a traditional eyeball.

You can read the article in a few minutes. But if you want a quick summary of where opsins have been found, some of the references included in the article will give you a good idea:

Arikawa, K., & Takagi, K. (2001). Genital photoreceptors have crucial role in oviposition in Japanese yellow swallowtail butterfly, Papilio xuthus. Zoological Science, 18, 175-179. http://dx.doi.org/10.2108/zsj.18.175

Pérez-Cerezales, S., Boryshpolets, S., Afanzar, O., Brandis, Al. Nevo, R., Kiss, Vl., Η Eisenbach, M. (2015). Involvement of opsins in mammalian sperm thermotaxis. Scientific Reports, 5, 16146. http://dx.doi.org/10.1038/srep16146

Ramirez, M. D., & Oakley, T.H. (2015). Eye-independent, light-activated chromatophore expansion (LACE) and expression of phototransduction genes in the skin of Octopus bimaculoides. Journal of Experimental Biology, 218, 1513-1520. http://dx.doi.org/10.1242/jeb.110908

Ullrich-Lüter, E. M., Dupont, S., Arboleda, E., Hausen, H., Á Arnone, M. I. (2011) Unique system of photoreceptors in sea urchin tube feet. Proceedings of the National Academy of Sciences, 108, 8367-8372. http://dx.doi.org/10.1073/pnas.1018495108

In summary, opsins, light-sensitive proteins, have been found in genitals, sperm, skin and feet. There is a lot more than what meets the eye going on here.

Click on the Start button beneath the spiral. Watch the spiral rotate for 30 seconds (it should automatically stop at 30 seconds). Once the spiral has stopped rotating, continue to watch it for a few seconds. Does it appear to expand even though it is perfectly stationary (unless you are having an earthquake)?

This is an afterimage. Remember when we stared at red and then looked at white and saw green? By staring at red, we had fatigued the red-green channel of opponent process theory. The fatigued caused the red-green channel to respond less vigorously than normal. When we looked at white, the red-green channel responded below baseline, which signaled green.

The same thing is going on here. We have neurons that are sensitive to motion in a particular direction. The rotating spiral causes some of those neurons to become active. By observing the rotating spiral for 30 seconds, we fatigue those neurons. When there is no motion, those neurons respond below baseline which signals motion in the opposite direction. Clockwise rotation of the spiral makes the sprial appear to recede. In the absence of motion, the fatigue direction sensitive neurons signal the opposite -- an expansion.

You're blind! Your're blind again! Old man Elvers is obviously crazy again. You can see perfectly well -- how else could you be reading this?

But you are blind for a brief period of time a couple of times per second whenever you are reading (unless you are using RSVP). In the lab, it is pretty easy to show that reading causes blindness. You need an eye tracker to detect when a person rapidly moves his or her eyes during reading. Such movements are called saccades and they occur when you move your eyes from one chunk of text to the next while reading. If you show the person something during the saccade, they will not see it because the visual system suppresses visual processing during the saccade.

Why does saccadic suppression occur and why don't we notice it? Saccadic suppression occurs because the eye moves so rapidly during the saccade that the retinal image is substantially blurred -- if you have ever been at an auto race, you know that the images of the cars are blurred as they speed past you. The same thing happens with the text that you are reading during a saccadic eye movement. (the blurry image says "The blurry image") would make it very difficult (and unpleasant) to read (I told you so). Thus, the visual system suppresses the processing of the image during saccades.

Why don't we notice the suppression during saccades? The visual system employs a type of memory, called iconic memory, to very briefly hold the last image. During saccadic suppression, the visual system uses the image stored in iconic memory to keep you from noticing the saccadic suppression.

The next time that some evil professor asks you to read too much in too short of a period of time, tell him or her that you can't and explain that reading causes blindness and that you value your vision too much to be blinded, even temporarily.

How much time could you save if you could read 400 (or more) words per minute and still have good comprehension and recall? I'm not talking about skimming, but rather reading each and every word in the passage. You can try it yourself by fixated (staring at) on the plus sign below and then clicking on the RSVP button:

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The words were presented one-by-one in the same location. That is called Rapid Serial Visual Presentation (What?! You thought RSVP meant répondez s'il vous plaît! Silly you.) Normally when we read, much of the time is spent planning where the eyes should move to next (in a rapid movement called a saccade -- maybe I'll tell you a weird fact about saccades tomorrow) and in moving the eyes to that part of the text. RSVP removes that planning and moving by presenting the words in the same location. With a little practice, people can read over 700 words per minute with RSVP (comprehension suffers at this rate).

Do the two circles appear to be (you already guessed that they are physically) the same lightness? For most people the left-hand circle appears much lighter than the right-hand circle. The RGB (red, green, blue / computer) representation of the circles are exactly the same. Even my cheap photometer reports them as the same lightness (111 lux on the monitor in my office).

One explanation for why the circles appear different was offered by Hans Wallach. Wallach claims that the lightness of achromatic (black, white, shades of gray) colors is determined by the ratio of the lightness of the object to the lightness of its surround. The larger the ratio, the lighter the object will appear. The surround of the circle on the left is darker (74 lux on my monitor) than the surround of the circle on the right (134 lux). Thus, the object:surround ratio for the circle on the left is 111:74 = 1.50 and the object:surround ratio of the circle on the right is 111:134 = 0.83. Thus, the circle on the left should, and does, appear brighter than the circle on the right.

Why should the perceived lightness of an object depend on the lightness of its surround? The answer is that how light an object is should not depend on how brightly it is illuminated. A light shirt should appear equally light whether it is in a dark room or bright sunlight. The illumination usually illuminates both the object and its surrounding background equally. Because of this, if the illumination doubles, the amount of light reflected from the object and it surround should both double. If both increase by the same proportional amount, taking the ratio of the two will cancel the proportion out, leaving the ratio constant. Thus, Wallach's ratio principle explains how the visual system maintains lightness constancy.

The figure violates the ratio principle's assumption that the illumination illuminates everything equally. The circle on the left can be interpreted as being in a lower level of illumination (its surround is dark) and the circle on the right can be interpreted as being in a higher level of illumination (its surround is lighter). When the assumption of equal illumination is violated, misperceptions can occur.

I tried coloring my little chick yellow, but I had a hard time staying in the lines. But wait! Look directly at the chick and back away from the screen. Keep backing up. At some distance (for me the visual angle of the chick was about one third of a degree) my coloring becomes perfect! No yellow outside the lines and all yellow within the lines!

There are a couple of things going on. The white background consists of short, medium and long wavelengths of light. The yellow of the chick consists of medium and long wavelengths of light. Thus, the difference is that the white has short wavelengths (primarily sensed by the S cones) and the yellow does not. Thus, we need the S cones in order to distinguish between the two.

The S cones are missing from the fovea where we have the greatest acuity. If we get the image of the chick to be primarily foveal (by looking directly at it and backing up sufficiently far) the visual system will not be able to distinguish where the yellow stops and the white starts. Based on top-down processing, the perception of the form of the chick provides the visual system with a strong clue about where the yellow should be (namely within the outline of the chick) and that is what we perceive.

In the late 19^th century Charles Benham created a top. The top was printed in black and white, yet when it was spun at the proper rate, colors (called Fechner colors) would appear. Below is a simulation of Benham's top. Since spinning your computer monitor is probably not a great idea, you can start the top spinning by clicking on the Start button below as long as you are not prone to seizures or are sensitive to flickering lights.

Some people are sensitive to flickering lights. In extreme cases, the right rate of flicker can induce a seizure. If you are sensitive to flickering lights or are prone to seizures, you should not click the Start button.

For more information on Benham's Top and to be able to customize your own top, visit this page.

I was looking through one of the general science websites that I often visit, Science News, and found the following picture of mountains on the moon:

When I saw that picture, I thought "If I turn it upside down, the mountains will turn into valleys." You can try it yourself by moving your mouse over the picture which should make the picture rotate 180°

Why did I think that that phantasm would occur and why does it occur? One of the monocular depth cues assumes that light comes from above. If that is true, the only way the shadows could form the way that they do in the upright picture is if the lighter areas (those with the specular highlights) were mountains. Likewise, if light still comes from above in the upside down picture then the pattern of highlights and shadows can only occur if the former mountains are now valleys.

The Kentucky Derby and perception seem like they would have very little in common. Usually that is true. However, this year's winner, Nyquist, shares his name with an important theorem in digital audio and human audition -- the Nyquist-Shannon Theorem (which sounds better than the Harry-Claude Theorem which is why they probably did not use their first names). In short, the Nyquist-Shannon theorem states that you need to take samples of an auditory (or any) waveform at twice its highest frequency in order to preserve the waveform. Since young, normal humans can hear up to approximately 20,000 Hz, digital audio needs to collect twice that many samples per second -- 40,000 samples per second. CDs and high quality digital audio are recorded at 44,100 samples per second. The next time you hear digital audio, think of both the Kentucky Derby and the Nyquist-Shannon Theorem.

You may have never heard of Claude Shannon but you have used stuff based on his work (and you are doing so right now). He also played a big role in the Human Information Processing paradigm in psychology during the 1960s through 80s.

Meet Miss Marple, formerly one of my buddies at the Humane Society of Greater Dayton. I say formerly because she was adopted a couple of days ago -- way to go Miss Marple!

One of Miss Marple's eyes is clouded over. This is likely due to cataracts on the lens. While she was likely able to see from the eye, her vision in that eye would be little more than a uniform field of a shade of gray. That means that her binocular vision was likely non-existent, and this would suggest poorer depth perception than if she had normal vision in both eyes.

However, her depth perception was really good. If you rolled her favorite toy, a small red ball with green and white stripes, past her, she would whack it with her paw every time -- she would be an excellent cat to have if you had a mouse problem. How can her depth perception be so good without binocular disparity? Remember that we (and cats) have all sorts of monocular depth cues and fortunately for Miss Marple, some of them, such as partial occlusion, are really useful for determining depth.

Rorqual whales, such as the blue whale and the fin whale, take giant gulps (over 100 cubic meters) of water when they feed on krill and plankton. How do they know when to open their mouth to gulp? In 2012, Nicholas Pyenson published an account of a newly discovered sensory organ in the chin of rorqual whales that is filled with mechanoreceptors which sense when things are bumping into the whale's chin. If there are enough food in the ocean bumping into the whale's chin, the mechanoreceptors sense the bumps and tell the whale to open wide. Here is a more complete summary.

I know that my former students of perception could not survive without the occasional tidbit of perception and/or a cute Humane Society of Dayton animal in need of a home. To help you cope with your withdrawal syndromes of no longer having 150 minutes per week of perception, I will, from time-to-time, post some odd thing that I have run across in my exploration of perception and life. Enjoy!