Introduction to Cognitive Science
Computational Theories of Consciousness

Vision (& Perception)

Last Update: 19 March 2014

Note: NEW or UPDATED material is highlighted

For instructions on how to access articles from certain journals (notably Psychological Review) from machines,
link to: "Classic (Online) Readings in Cognitive Science"

"[T]he task of the brain, when viewed from a certain distance, can seem impossible: it must discover information about the likely causes of impinging signals without any form of direct access to their source. …[A]ll that it ‘knows’, in any direct sense,…[is] the ways its own states (e.g., spike trains) flow and alter. In that (restricted) sense, all…[it] has direct access to is its own states. The world itself is thus off-limits. …Notice how different this conception is to ones in which the problem is posed as one of establishing a mapping relation between environmental and inner states. The task is not to find such a mapping but to infer the nature of the signal source (the world) from just the varying input signal itself. [§1.2, p. 183.]

"If ["perception is indirect" (J. Hohwy, "Functional Integration and the Mind", Synthese 159(3) (2007): 315–328)]…, then the role of perceptual contact with the world is only to check and, when necessary, correct the brain's best guessing concerning what is out there.

"Nevertheless, we may still reject the bald claim that ‘what we perceive is the brain's best hypothesis.’ …[W]hat we perceive is not some internal representation or hypothesis but (precisely) the world." (§4.4, p. 200.)

"[T]he brain is a creativity machine, which obtains incomplete information from the outside world and completes it."

"[T]hese findings [about "neural correlates for illusions involving senses other than vision, such as hearing and touch"] demonstrate that we have no direct contact with reality. Our brain is always abstracting and interpreting the world around us."

"Open a standard textbook on neurobiology and you will find somewhere an illustration with an eye on one side and the primary visual cortex on the other. Signals flow from the eye's retina to the optic chiasm; then on to the lateral geniculate, explained as a kind of way station; and then to the primary visual cortex. It is a comfortable diagram. We engineer such systems, with a few modules lined up from left to right, with information flowing through them.

The trouble is, neurobiology textbooks also note that 80% of the input to the lateral geniculate comes from somewhere other than the retina. A good deal comes down from the primary visual cortex, suggesting that vision is a matter of guided hallucination. Other substantial input comes from auditory apparatus. Everything is all mixed up, with information flowing bottom to top and top to bottom and sideways too. It is a strange architecture about which we are nearly clueless."

"Light bouncing off stuff is what we see."

"The ‘magic’ of consciousness is that we think we are experiencing the world through our eyes and ears, but really everything is seen and heard in the brain."

"Reality is a tape-delayed broadcast, carefully censored before it reaches us."

"Our perceptions…are fantasies we construct that correlate with reality."

"Your brain, after all, is encased in darkness and silence in the vault of the skull. Its only contact with the outside world is via the electrical signals exiting and entering along the super-highways of nerve bundles. Because different types of sensory information (hearing, seeing, touch, and so on) are processed at different speeds by different neural architectures, your brain faces an enormous challenge: what is the best story that can be constructed about the outside world?"

"My phenomenal world…[is] a neural fiction perpetrated by the senses."

"It is a gross mischaracterization to say that we simply open our eyes and take it all in; what we are in contact with is a constructed product of many different brain processes."

"Biological systems have available through their senses only very limited information about the external world. Yet these systems make strong assertions about the actual state of the world outside themselves. These assertions are of necessity incomplete. Clearly, a [complete] replica of an object and its qualities cannot be embodied within the brain. How can an incomplete description, encoded within neural states, be sufficient to direct the survival and successful adaptive behavior of a living system?"

  1. The visual system in the brain:

    1. retina

      • Figure 06-03. The eye. (a) Illustration showing how objects in the environment are physically projected to the back of the eye&151;the retina. (b) The eye and a cross-section of the retina. The cross-section of the eye shows where the photoreceptors are located in the retina. Both the rods and cones are shown. They respond to different types of light. The neural signal then travels via bipolar cells and then to the ganglion cells. The axons of the ganglion cells take the neural information out of the eye and backward toward the cortex. Source: Squire et al., 2003.

    2. from retina to cortex

      • Figure 06-07. The visual pathways from retina to cortex. (a) Example of a brain slice from a functional magnetic resonance imaging (fMRI) scan, showing the lateral geniculate nucleus (LGN) and primary visual areas at the back of the brain (the occipital cortex). The two different colors denote the two hemispheres of the brain. (b) Schematic illustration showing the visual pathways from the retina in the eyes to the primary visual cortex at the back of the brain. You can see here that the neural information from the nasal or inner sides of the eyes crosses over at the optic chiasm, to be processed in the contralateral side of the brain. The left visual field, in blue, is processed by the right visual cortex (also blue). The LGN, displayed in green, relays the visual information to the primary visual areas of the cortex. Source: Squire et al., 2003.

    3. hierarchy of visual processing

      • Figure 06-10. The hierarchy of visual processing. A demonstration of the hierarchical response properties of the visual system to simple and complex stimuli. The leftmost column shows our house stimulus and what receptive fields of each visual area we would see in the balloons. Not only do the receptive field sizes increase in each visual area, but also the complexity of the shapes they respond to. The rightmost column shows an estimate of where each area is in the brain. You can see that early visual areas respond to simple features and, as we move along the processing stream, areas respond to more complex shapes and objects. This is a well-established theme of the visual system.

  2. From "Neuroscience and Behavior Links" at UB's "Neuroscience and Behavior Explore—Learn—Enjoy" page:

  3. Lamb, Trevor D. (2011), "Evolution of the Eye", Scientific American 305(1) (July): 64–69.

  4. How Saturn with its rings looked to early astronomers

  5. Gibson, James J. (1979), The Ecological Approach to Visual Perception (Boston: Houghton Mifflin).

  6. Fodor, Jerry A.; & Pylyshyn, Zenon (1981), "How Direct is Visual Perception? Some Reflections on Gibson's 'Ecological Approach' ", Cognition 9: 139-196.

  7. Marr, David (1982), Vision: A Computational Investigation into the Human Representation and Processing of Visual Information (New York: W.H. Freeman).

  8. Biederman, Irving (1987), "Recognition-by-Components: A Theory of Human Image Understanding", Psychological Review 94: 115-147.

  9. Gregory, Richard L. (1997), Eye and Brain: The Psychology of Seeing, 5th Edition (Princeton, NJ: Princeton University Press).

  10. Hayes, Brian (1999), "Seeing between the Pixels", American Scientist 87(May-June): 202–207

  11. Simons, Daniel J. (2005), Visual Cognition Lab

  12. Changizi, Mark A.; Hsieh, Andrew; Nijhawan, Romi; Kanai, Ryota; & Shimojo, Shinsuke (2008), "Perceiving the Present and a Systematization of Illusions", Cognitive Science 32(3) (April-May): 459–503.

  13. Cyclopean vision example

  14. Vision in Non-Human Animals:

  15. On Hearing & Sound:

    1. One of the earliest, if not the original, sources of "If a tree falls and no one hears it, does it make a sound?" (with a local, Western New York connection):

    2. "Sounds are made in…mechanical pressure waves, which is a fancy way of saying sound is a bunch of pushes through something like air. When those pushes get to your ears, your brain turns them into things you hear." —Church, Jok (2012), "Beakman Jax" (comic strip), Buffalo News (29 July).

    3. Hoy, Ronald R. (2012), "Convergent Evolution of Hearing", Science 338 (16 November): 894–895.

      • Discusses how human (and insect) ears work.

  16. On Pain:

  17. Can Plants (and other non-higher-animal biological organisms) Sense?:

Text copyright © 2007–2014 by William J. Rapaport (
Cartoon links and screen-captures appear here for your enjoyment.
They are not meant to infringe on any copyrights held by the creators.
For more information on any cartoon, click on it, or contact me.