The internet provides a universe of learning resources, and students of perception are among the beneficiaries of these resources. This web directory provides links to many websites relevant to Blake and Sekuler's Perception, 5th Edition. Some of the links afford expanded illustrative coverage of concepts described in the textbook, and other links take you to webpages with demonstrations of visual and auditory phenomena (some of those demonstrations may require special browser plug-ins that play animations - you will be told by your web-browser whether a plug-in is needed). We will update this website regularly, adding new material and pruning the inevitable broken links. If you find a useful website not listed here, just email the URL to us and we'll see about adding it.
To help students of perception, we've organized this web directory according to chapters in the textbook.
Philosopher Thomas Nagel's famous essay on knowing what it's like to be a bat. His essay underscores the logical barrier we face whenever we struggle to understand the perceptual world of another creature.
Bats emit high-pitched calls, some used for social communication and others used for echo-location (described in Chapter 11). Hear samples of bat calls, some that have been acoustically modified to bring normally inaudible acoustic events into your audible range.
Throughout the text readers encounter human brain mapping results obtained using the technique called functional magnetic resonance imaging (fMRI). Here is a relatively non-technical explanation of what is actually measured in an fMRI experiment.
In the Charles Bonnet syndrome visual hallucinations are experienced by blind people. The C.B.S. is as fascinating as it is perplexing.
Perception is a topic that forces students to think about the mind/body problem, an age-old philosophical issue. This website gives you definitions of terms encountered when talking about the relation between mind and brain (including definitions of dualism, skepticism, realism).
Can humans perceive things that fall outside of awareness? This controversial subject -- subliminal perception - and the evidence bearing on its existence are critiqued here and here.
Illusions figure prominently in the study of perception. Here are some excellent websites where you can experience illusions (in some cases interactively) and read more about the bases of illusions. Michael Bach's site adopts a broad definition of illusion. Nice selection of Auditory and visual illusions, with some explanations of each, and nice demos, some interactive
Peter Kaiser (York University, Toronto, Canada) has developed a webbook on vision, with lots of useful definitions and illustrations.ContentsVision research is replete with numbers describing visual structures (e.g., the number of fibers in the optic nerve). Here are many of those numbers, organized in a single list.
Within the animal kingdom one find huge variety in the design of eyes. Here's a website that provides a good sample of some of those eyes.
An interesting look at some light's basic properties, and their impact on images and vision.
The eye's optical components are responsible for focusing images on the retina. For a nice introduction to ocular optics take a look at these two websites, here or here. The first one says it's for kids, but don't be fooled. For a thorough history of the study of optics, including an interesting account of the invention of spectacles, take a look at this website.
For useful information on optical accomodation and refractive error.
It's a clouding of the lens, and this common problem affects more than half of all over 80 years of age in North America. It's a cataract, of course. Learn what it is.
Presybopia (the age-related increase in the near point of vision) and strategies for managing it.
Perhaps you've experienced them -- floaters - those little black specks that you may occasionally see. Here's an explanation of what they really are.
The facts about age-related macular degeneration, a leading cause of blindness.
A fact sheet on glaucoma.
United States Food and Drug Administration information on LASIK surgery, a procedure for reshaping the cornea to correct refractive error.
A thorough, beautifully illustrated tour of the eye's retina (with bonus material on color vision and on psychophysics).Back to ContentsWilson Geisler's (University of Texas) website demonstrates the visual consequence of the human retina's uneven spatial resolution:
Delightful, intriguing illusions of lightness created by Edward Adelson and his colleagues at MIT.
A compelling animation showing a context effect in lightness perception (Barton L. Anderson, Jonathan Winawer (2005) Image segmentation and lightness perception. Nature, 434, 79 - 83).
Interactive demonstrations of the Hermann grid illusion. This site allows you to vary several parameters of the grid and see how the illusion is strengthened or diminished.
The concept of the receptive field is central to understanding vision and visual neurophysiology. For useful material on receptive fields go here.Jody Culham (University of Western Ontario) has put together a very nice overview of brain areas involved in vision, including detailed images.
Matthew Schmolesky of the University of Utah vision group has created a richly illustrated website devoted to the primary visual cortex (V1), and it includes wonderful anatomical images and helpful diagrams.
Chapter 4 describes efforts to create a prosthetic device that could provide vision to previously blind people. The device would electrically stimulate the visual cortex, using patterns of stimulation sent by a head-mounted camera. One of the research groups working on this technology, at the Illinois Institute of Technology, has a website explaining how this technique could work.
Recent evidence from brain imaging studies implies that visual cortex can be "recruited" by other sensory modalities when normal ocular input to visual cortex is lost, due to eye disease. This news story describes one such study, and this website summarizes another.
Dyslexia is a developmental disorder characterized by difficulties with accurate and/or fluent word recognition. While not necessarily the cause of dyslexia, abnormalities in the visual cortex seem to be associated with the occurrence of the condition according to a Stanford University brain imaging study.
NASA's robot explorer Spirit, described in Chapter 5, faces the challenge of navigating unfamiliar terrain and photographing what it sees. For an update on Spirit's activities, check out this NASA website.At this webpage you can try your hand manipulating the sizes of the "blocks" used in the "block masking" procedure illustrated in Figure 5.25, page 174.
Fourier Analysis is discussed in Chapter 5 (Spatial vision) and in Chapter 10 (hearing). For web resources and demonstrations about Fourier analysis go here. For a more detailed, but still accessible treatment of Fourier analysis, get Larry Thibos' webbook.
As discussed in Chapters 3 and 5, it is generally believed that neurons in the retina and subsequent, early stages of visual processing have receptive fields with center/surround organization. This receptive field layout makes each neuron maximally responsive to contours of a given size or, in the parlance of Fourier Analysis, to a limited range of spatial frequencies. One elegant, simple mathematical description for such receptive fields characterizes them as Gabor filters, and you can read about this unique spatial representation (and can produce your own Gabor filters) at this website. Gabor filters, incidentally, were named after the Nobel prize-winning physicist Denis Gabor -- it was Gabor who proved mathematically that resolution in frequency and resolution in time involve competing demands when trying to measure complex signals such as sound waves. He went on to describe a compromise measurement solution that optimizes resolution in both domains, and his ideas were later generallized to the spatial domain in vision. We honor his contribution by referring to neurons selective for spatial frequency as Gabor filters.
When it comes to understanding spatial vision nothing beats seeing your own contrast sensitivity function, and you can do this by viewing the test figure available here.
Want to know more about Gestalt principles? Here's the place. And for some exercises showing Gestalt principles of proximity and similarity, try this website.
Gestalt principles can be applied to commercial visual design, including web pages. To see how, go here or here.
Chapter 6 discusses Biederman's recognition-by-components theory of object recognition, and this website provides additional details (the site focuses on vision in birds, but the principles are exactly the same as those encountered in human object recognition).
Human faces are among the most conspicuous familar "objects" in our daily lives. And among the most bizarre neurological conditions is the loss of ability to recognize familiar faces consequent to brain damage to a specific region of the occipto-temporal lobe. This condition, known as prosopagnosia, can be explored here or here.
The question of whether there exists a brain area specialized for face perception has generated conflicting evidence and heated debate.The text gives evidence for the view that the so-called "face area" is, in fact, more generally devoted to visual expertise and categorization. Nancy Kanwisher, Harvard University, presents evidence in favor of the view that this brain area is indeed specialized for faces. We anticipate that his question will receive considerable attention during the next few years.
Here are some objects - Greebles -- you probably never saw before reading about them in Blake &Sekuler's textbook. They may strange at first, but with practice, you can learn to recognize individuals from this unusual "species." Take a look at this webpage to see some more greebles and learn how these unusual creatures are contributing to understanding of object recognition.
Your attention cannot be focused at two different places at once. Consequently, you may fail to see normally conspicuous objects or events, such as a gorilla walking past you you. Sound incredible? Here are some demonstrations of inattentional blindness.
Related to inattentional blindness is the attentional blink: an inability to see the second of two "target" items presented in rapid succession (it is as if your attention temporarily "blinks" off following the appearance of the first target, causing you to miss the second one when it occurs very shortly thereafter.) To experience the attentional blink, navigate to this website and follow the instructions. You will receive 30 trials on a rapid serial visual presentation task, and at the end of the 30 trials you will be shown your results. The attentional blink will show up as "missed" second targets for the brief "lag" time between two successive targets.
Back to ContentsUnderstanding of color vision has advanced to a point where a quality of human experience - color vision - can be related to short DNA sequences on a single chromosome. For an up-to-date overview of the genetics of color vision (including color disorders), check out this.
Some nice demonstrations of aspects of of color vision, including color contrast.
One way vision scientists learn about color and its underlying bases is by studying color afterimages. To see a particularly compelling demonstration of colored afterimages, take a look at this website.
What does the world look like to a person with deficient color vision? These two websites try to simulate the experience: Here or here.
Random dot stereograms were invented by Bela Julesz, an engineer then at Bell Telephone Laboratories. Julesz wanted to see if people could see stereoscopic depth using figures that contained no recognizable form. We can, as demonstrated by stereopsis from these specially constructed stereograms. Chapter 8 includes stereo-pairs demonstrating stereopsis from random-dot stereograms, and red/green versions of those can be found at this website.Back to ContentsBuilding on the work of Julesz, Christopher Tyler (Smith Kettlewell Eye Reserch Insitute) invented what he called autostereograms. Tyler's basic approach has been modified to create the "magic eye posters" that have been popular recently.
Chapter 8 contains lots of figures illustrating depth cues, and you can see even more demonstrations (including some animations) at this website.
One particularly compelling illusion involving depth is called the "hollow mask" illusion. A concave mask or mould of a face appears convex when viewed with shading, and when the mask moves the this misperception of the depth relations in the mask creates reversals in perceived direction of rotation. For a good demonstration of the hollow mask effect navigate to this website. And at this website you can download the materials for creating your own version of the illusion, this one dubbed the dragon optical illusion.
Alcohol impairs depth perception, and this news story describes the research underscoring this impairment and one reason why it might occur.
The web is loaded with pages containing photographs of natural scenes in which depth is vividly portrayed by one or more of the monocular depth cues described in Chapter 8. Just do a Google search for depth perception, or for starters take a look at this website.
Chapter 8 also describes binocular rivalry, the breakdown in stable binocular single vision that occurs when radically different pictures are viewed separately by the two eyes. This webpage contains some demonstrations of binocular rivalry, and a more complete description of the phenomenon can be found here.
The Muller-Lyer illusion (page 313) is thought to result from implied depth cues in the figure causing an illusory change in the length of a line. You can experience the Muller-Lyer illusion and study factors that influence its magnitude using the interactive demonstrations at this website.
Back to ContentsWith the development and refinement of computer technology for creating video animations, the field of visual motion perception has exploded. A wbesite with some terrific demonstrations of motion perception phenomena.
We are remarkably adept at recognizing human activity, even when that activity is portrayed using just a handful of light spots attached to the limbs and torso of the body of an actor. Hard to imagine? Here are several sites with demonstrations of biological motion. Site One, two, three, four and five.
Any time you move about through the environment, you produce optic flow. Researchers study perception of optic flow using computer animations; here are some interactive demonstrations of optic flow.
How do you figure out where someone else is looking? Here are some techniques for measuring gaze position and eye movements.
Motion perception is influenced by the shape of the object in motion. Some demonstrations, crafted by McDermott, Weiss and Adelson, of this shape-motion interaction.
A stationary object appearing within a field of moving objects can disappear from view for several seconds at a time. Called motion-induced blindness, here are demonstrations of this remarkable phenomenon.
A sound wavelength calculator will give you the wavelength of any airborne acoustic frequency in inches, feet and meters.Sinewaves can be combined to produce acoustic signals that mimic human speech. Here's a site that explains how this works. And here're sites that demonstrate sinewave speech: Site one and Site Two.
Information about cochlear implants (including audio demonstrations of the sound quality available with these prosthetic devices). Go here, here or here.
Animations that simulate the ear's key mechanical and neural events.
Bats emit "calls" some of which contain frequencies that exceed the upper limits of human hearing. Researchers can reformatted some bat sounds --shifting them down in frequency-- so that humans can hear them. Give a listen.
Turn your house into a musical instrument: a case study in environmental acoustics.
Here's a site from you which you can download a huge variety of different sounds (searchable using a search-engine interface).
The glass Armonica is a most unusual musical instrument. Here are examples of sounds produced by this instrument, and here's why it is no longer played.
A nice essay from the journal Physics Today on sound localization. This journal, by the way, is published by the American Institute of Physics.
Back to ContentsGreat resource page with links to lots of sites dealing with music perception
Vocal tract and acoustics.Overview of vocal tract and acoustics of voice
Vocal cords in action.Includes movies of vocal cords and vocal tract in action.
Do it yourself sonification This website allows you to input a photograph or image of your own making and then experience it as a sonified representation.
Speech-like sounds can be synthesized by combinations of just a few sinewave signals. Called "sinewave speech" these synthesized utterances may initially be unintelligible, but once you know what the speaker is trying to say, you can then recognize the utterance. Here and here.
Here's a website where you can experience the McGurk effect, wherein visualization of a speaker's mouth influences what you hear the speaker saying.
Mothers unwittingly speak to their infants with a higher pitch to their voices. Examples of "motherese" being spoken.
Learn more about absolute pitch perception and other interesting aspects of musical experience.
Mondegreens are amusing errors in auditory perception: they are popular words, phrases or songs that are misperceived. Thus for example, "from sea to Chinese sea" in the song American the Beautiful would constitute a mondegreen. Here are some classic mondegreens.
Listen to the laughs discussed in Chapter 12.
Examples of computer synthesized sounds in which pitch height and pitch chroma vary.
Back to ContentsSome rare individuals cannot feel pain. Learn about the condition that causes this deficit here.
Whiskers are amazingly useful structures for allowing an animal to explore its environment through the sense of touch. Learn something about what our species misses by not having whiskers, here or here.
Want to know more about the phantom limb phenomenon? Here's a site that provides a historical overview, and here's another site that discusses theories of and treatment for the pain that can accompany phantom limb.
Instructions for creating your own no fuss, no muss phantom limb.
The force needed to move an object with your hand depends on the geometry of the surface over which the object is being moved. Experience the relation between force and surface layout, by trying these demonstrations.
Proprioception, the so-called 6th sense that we're largely unaware of, specifies where our body and limbs are relative to one another, and signals the amount of effort we're expending to engage in activities. In one of the rarest of all sensory disorders, proprioception can be abolished consequent to viral infection, and this case study of a person with this condition reveals just how important this 6th sense really is.
A highly readable, informed overview of the sense of smell, with brief treatments of on olfactory receptors, odor recognition and memory for odors.An overview of olfaction, including helpful diagrams and lots about the chemistry of olfaction.
Is human sexual behavior influenced by pheromones? Do we have a special vomero-nasal organ for registering the presence of pheromones? Learn what is currently believed by navigating to this website.
Recent experiments verify that dogs are able to detect cancer cells by smell. See this also.
Answers to frequently asked questions about smell.
Website with lots of links to material on taste and smell.
Healthcare professionals can use odors to diagnose disease. This webpage describes the telltale characteristic odors of different diseases.
Are you a supertaster? Find out by trying the exercise described here.
What is umami, and how does it contribute to taste?
Link to the webpage for the International Society for Psychophysics, where you'll find many interesting historical tidbits and links to pages with useful, detailed descriptions of techniques of psychophysics.
Some excerpts from Gustav Theodor Fechner's Elements of Psychophysics translated in English.
An accessible mathematical description of the multidimensional scaling.
This website has many exercises that deploy various psychophysical techniques, including one set of exercises that contrasts the method of constant stimuli, method of adjustment, and two versions of the staircase technique. The website also has great demonstrations of afterimages, apparent motion, visual search and the blindspot.