Cog~01&02VisPerc - visual perception the minds...

visual perception : the mind’s interpretation of visual stimuli

In early stage of visual perception, objects are distinguished from background.
This is usually not too difficult.
One of several exceptions: an object looks like the background (camouflage )

Rubin face/vase illusion
In figure-ground reversal , object and background can swap
(figure roughly means object, and ground means background)

M. C. Escher (1898-1972)
Another instance of figure-ground reversal.

Do you see an object in the background?

Once an object is located, it must be recognized.
Object recognition is aided by multiple processes.
Demo. Prepare to read the words that briefly appear in the box below.
Here is what you saw:

Preceding example demonstrates two kinds of perceptual processes:
bottom-up processes rely on the stimulus
The letter between C and T looks like a cross between A or H.
top-down processes rely on expectations (which depend on knowledge)
The letter between C and T cannot be an H.
These two kinds of processes work in concert.

The “THE CAT” demo is an illustration of one kind of
context effect
perception of stimulus is affected by surrounding stimuli
Examples
EGG = EGG
Obscured text
FUN = FUN
EAT = ?
Sloppy handwriting
What letter is this?

More context effects
Radenig snetneecs taht ilcndue wrdos wtih rarergaend lteerts is
psobslie if the frsit and lsat ltretes are not mvoed.

More context effects:
An excerpt from a magazine ad:
L ke y ur b ain, the n w L nd Rov r autom tic ly adj sts to anyth ng.
Who is standing behind Bill Clinton?

Another context effect:
Experiment
Ss saw underlined letter that appeared alone or as part of word .
K DARK
Letter and word presented very briefly, and Ss tried to name the letter.
Result: Accuracy was greater when letter appeared as part of a word.
This is the word superiority effect .
(Reicher, 1969)

Another context effect:
Experiment
Ss listened to audiotape of sentences with missing phoneme.
Sample Stimuli
The *eel was on the axle.
The *eel was on the shoe.
After each sentence, Ss repeated what they heard.
Results: Ss “replaced” appropriate phoneme.
Sample Responses
The wheel was on the axle.
The heel was on the shoe.
This occurred even though missing phoneme preceded contextual cue.
This is the phonemic restoration effect .
(Warren, 1970)

Object recognition is sometimes aided by light and shadow.
Example.
Which dimples appear to
be raised toward you?
Why?
Light usually shines from above.
(image from O’Reilly www.oreilly.de/catalog/9780596007799/toc.html )

Object recognition is sometimes aided by motion.
Example from Donald D. Hoffman
www.cogsci.uci.edu/~ddhoff/Sphere3.html
Example from Michael Bach
michaelbach.de/ot/mot_biomot/index.html
Elaborate Example from Nicholas Troje
www.biomotionlab.ca/Demos/BMLwalker.html
(G. Johansson, 1973)

Once an object recognized, the mind tries to determine how far away it is.