Chapter 21

Key Terms

Visual perception: the processing of visual information to see objects in the world.

CAPTCHAs: Completely Automated Public Turing tests to tell Computers and Humans Apart involve identifying distorted visual stimuli; they are typically very hard for machines to solve but relatively easy for humans.

Law of Prägnanz: the notion that visual perception will tend to be organised as simply as possible.

Figure-ground segregation: perception of the visual scene as consisting of an object or figure standing out from a less distinct background.

Monocular cues: cues to depth that only require the use of one eye.

Linear perspective: a strong impression of depth in a two-dimensional drawing created by lines converging on the horizon.

Texture gradient: a depth cue provided by the increased rate of change in texture density of a slanting object from the nearest part to the furthest part.

Interposition: a depth cue in which a closer object partly hides another object further away.

Motion parallax: a depth cue provided by the movement of an object’s image across the retina.

Binocular cues: depth cues requiring the use of both eyes.

Stereopsis: a depth cue based on slight differences in the images on the retinas of the two eyes.

Oculomotor cues: depth cues based on contractions of muscles around the eye.

Accommodation: a depth cue involving a thickening of the eyes’ lenses when focusing on close objects.

Convergence: a depth cue provided by greater inward turning of the eyes when looking at a close object than one further away.

Geons: basic shapes or components combined in object recognition; an abbreviation for ‘geometric ions’ proposed by Biederman.
Viewpoint-invariant perception: the notion that it is equally easy to recognise objects from many different viewpoints.

Viewpoint-dependent perception: the notion that objects are easier to recognise from some viewpoints (especially typical ones) than from others.

Visual illusions: drawings or other visual stimuli that are misperceived by nearly everyone.

Ames room illusion: the room looks like an ordinary room but actually has a very unusual shape; this causes distortions in the apparent heights of individuals standing in front of the rear wall.

Inattentional blindness: the failure to perceive the appearance of an unexpected object in the visual environment.

Change blindness: the failure to detect that a visual stimulus has moved, changed, or been replaced by another stimulus.

Misdirection: a form of deception practised by magicians in which the audience’s attention is focused on one object to distract its attention to another object.

Weblinks

A wide range of materials, including videos and demos, on cognitive psychology and cognitive neuroscience
http://www.gocognitive.net/

Summary of Gestalt theory
https://www.learning-theories.com/gestalt-theory-von-ehrenfels.html

A video about the law of Prägnanz
https://www.youtube.com/watch?v=m8OBqPwgtYU

Examples of the Gestalt principles and their use in graphic design
http://homepages.ius.edu/RALLMAN/gestalt.html

A video about depth perception
http://www.youtube.com/watch?v=ZNmEUhvFxtM&feature=related

The Müller-Lyer illusion
https://www.youtube.com/watch?v=Ub10aZeLKfg

Some visual illusions
http://psylux.psych.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/hall_of_illusions.html

A video of the Ames room illusion
https://www.youtube.com/watch?v=gJhyu6nlGt8

Video of an optical illusion – two lines, one height
http://www.youtube.com/watch?v=QpL7ROdpGZo

Dan Simons’ home page, with more about his research including videos of the invisible gorilla!
http://www.dansimons.com/index.html

Change blindness: A demonstration of the colour changing card trick
http://www.youtube.com/watch?v=voAntzB7EwE

Mather, G. (2009). Foundations of sensation and perception (2nd ed.). George Mather provides good introductory coverage of most of the topics discussed in this chapter. For example, Chapter 10 is devoted to depth perception
http://www.routledge.com/books/details/9780415581813/