Sensation and Perception Final

Why is depth perception difficult?

Our world is 3D, and our retinas are 2D

oculomotor cues

using information from the actions of the muscles to determine how far away things are in depth

pictorial depth cues

relative and familiar size, overlap, shading, height

looming

as something gets closer to you, the visual area gets larger and larger

binocular disparity

the difference in the retinal images of the two eyes that provides information about depth

binocular disparity is most useful for...

things within 6 meters

two stages of binocular depth perception

stage 1: solving the stereo-correspondence problem

stage 2: calculating the retinal disparity

stereo correspondence problem

the task of measuring the disparity between the two matching image points in each eye

auto-stereograms

illusions caused when the eye solves the correspondence problem incorrectly

* images with repetition in them

3 possible outcomes of calculating the retinal disparity

* zero disparity
* crossed disparity
* uncrossed horopter

Panum's area of fusion

the region of small disparity around the horopter where the two images can be fused into a single perception

Strabismus

can be caused by problems in the extra-ocular eye muscles, the neutrons that enervate the eye muscles, or problems in the part of the eye that directs eye movements and the person becomes cross-eyed

amblyopia

lazy eye caused by one eye having much worse acuity than the other

* brain starts supressing info from worse eye
* must be corrected early or proper depth perception may never develop

dimensional ambiguity

different actual size can produce the same size retinal image and vice versa

Emert's Law

the idea that the perceived size of an after image varies based on the projection surface

Ponzo illusion

An illusion of size in which two objects of equal size that are positioned between two converging lines appear to be different in size. Occurs because you can’t help using depth cues telling you that the top bar must be bigger

when do you lose size constancy scaling?

if the depth cues are missing or misleading (ex: Ames room)

shape constancy

the tendency to interpret the shape of an object as being constant, even when its shape changes on the retina

how is shape constancy achieved?

depth factored in when interpreting object shape

spatially serial

one area at a time

spatially parallel

everywhere at the same time

three stage model of object perception

stage 1: low level vision

stage 2 : visual routines

stage 3: visual cognition

low level vision

recognizing simple features using a bottom-up approach and finding discontinuities (differences in brightness or colour to define edges) in a spatially parallel field

what happens without change

object becomes invisible if it stays on the same spot of the retina fro too long (ganzfeld)

* our eyes have a slight shiver to prevent this

Gestalt principles of organization

similarity

proximity

continuity

closure

connectedness

things that influence seeing figures

* figure is more likely to be seen is low in visual field
* figure has high spatial frequency information
* figure is more likely convex
* figure is meaningful or fits expectations

visual routines

focusing on one area at a time (spatially serial) to attend to the object

overt orienting

when we want to attend to something we make an eye movement toward that item so we can have the image of the object fall on the fovea in order to see things in high detail (slower, after)

covert orienting

the movement of attention from one location to another without moving the eyes/body (faster, first)

advantages of attending to something

* attended thing is seen more quickly and accurately
* seen in higher detail

Tichener's Law of Prior Entry

if two things happen at the same time, the thing you were attending to seems to happen first

visual cognition

The ability to process visual information through top down processing by integrating to form object recognition.

where object file for current scene is matched to a representation in long term memory to see if the object is recognized as something that has been seen before (ex. last time I saw a black fluffy thing it was a dog)

problem in visual cognition

the retinal image is ambiguous. there may be many interpretations

Helmholtz

perception as unconscious inference

Ullman

visual routines are operations carried out on the image used to derive the spatial relations between selected parts of an image

illusory conjunctions

when attributes of one object drift onto another (ex. gun focus in eye witness testimonies) (ex. seeing a woman + a man with a beard, thinking you saw a woman with a beard)

integrative agnosia

can't combine attributes to make an object file (spatial relation problems)

ex: person trying to draw a person but the body parts are not connected properly

Simutagnosia (Balint's Syndrome)

inability to perceive more than one object at a time

real motion

actual motion of an object

apparent motion

static motion ex: tv

disco stroboscopic effect

the strobe lights has an affect on the perception of movement. During the flash you see one image and when the flash is off you do not see it and then it flashes again and you see a new image

depth perception

ability to judge distance and 3D relations

visual angle

area covered on the back of the retina

atmospheric perspective

a lighting-based depth cue - the farther away an object is, the more air the light must pass through to reach us and the more that light can be scattered, with the result that distant objects appear less distinct than nearby objects

texture gradient

object elements get more condensed the further you are

binocular cues

clues about distance based on the different views of the two eyes

stereoscope

a device for presenting one image to one eye and another image to the other image

stereopsis

three-dimensional vision

autostereogram

person fuses different parts of the same picture to achieve 3D perception

oculomotor

cues based on our ability to sense the position of our eyes and the tension in our eye muscles

convergence cues

inward movement of the eyes when we see close up things

strabismus

crossed eyes

non-corresponding points

images of the objects that are not on the horopter

binocular depth cues

neutrons that respond to absolute disparity

absolute disparity

the visual angle between the images of an object on the two retinas

size constancy

Our perception of an object stays relatively constant, even at different distances (we don't believe someone got shorter when they are farther away)

misapplied size constancy scaling

doesn't work in a 2D image

Ponzo Illusion

An illusion of size in which two objects of equal size that are positioned between two converging lines appear to be different in size. Also called the railroad track illusion.

moon illusion

An illusion in which the moon appears to be larger when it is on or near the horizon than when it is high in the sky.

apparent distance theory

things on the horizon appear larger and get smaller as they raise vertically

Panum's fusion

fuse left and right image to get 3D

binocular rivalry

the competition between the two eyes for control of visual perception, which is evident when completely different stimuli are presented to the two eyes

Cheshire Cat illusion

an example of binocular rivalry

Ambylopia

lazy eye causing the other eye to lose some portions of vision

who doesn't see the tilt after effect

people without binocular vision

what type of visual deprivation is damaging

early deprivation

ocular dominance columns

cortical columns consisting of neutrons that receive signals from the left eye only or right eye only

visual scanning

movement of the eyes from one location or object to another

fixation

focusing on one object or person to recognize it

saccadic eye movement

a rapid, jerky movement from one fixation to another

how many times per second do you move your eye

3 times

overt attention

attention that involves looking directly at the attended object

covert attention

attention without looking

visual salience

areas of stimuli that attract attention due to their properties/difference from background

attentional capture

attention involuntarily drawn to something

salience map

a spatial layout that emphasizes the most behaviourally relevant stimuli in the environment

scene schema

knowledge of what a given scene typically contains

attention is influence by...

goals and interests

spatial attention

attention to a specific location

Posner

information processing is more effective at place where attention is directed

illusory conjunction

combinations of features from different stimuli

Balint's syndrome

a conditions caused by brain damage in the parietal lobe in which a person has difficulty focusing attention on individual objects

visual search

looking for a target object amongst other objects

conjunction search

scanning display in search of specific location

dual-task procedure

an experimental procedure in which subjects are required to carry our simultaneously a central task that demands attention and a peripheral task that involves making a decision about the contents of a scene

visual agnosia

inability to recognize objects

Simultagnosia

inability to perceive more than one object at a time

grouping by Pragnaz

every stimulus is seen as simply as possible

akinetopsia

motion blindness

image displacement signal

In corollary discharge theory, the signal that occurs when an image moves across the visual receptors.

motor signal

In corollary discharge theory, the signal that is sent to the eye muscles when the observer moves or tries to move his or her eyes.

corollary discharge signal

a copy of the motor signal that is sent to the eye muscles to cause movement of the eye. The copy is sent to the hypothetical comparator of corollary discharge theory

motion perception beings in which part of the brain

the striate cortex

swinging room experiment

optic flow created by walls hanging from chains. showed optic flow information is very important to balance;

misleading optic flow information can cause babies to fall over and adults to sway and have to brace themselves

stroboscopic motion

illusion of apparent movement; result from flashing a series off still pictures in rapid succession

Aubert-Fleischl Effect

underestimate speed and distance when tracking

ex: the clock pendulum

where does the neural processing of motion start?

magno cells

corollary discharge theory

when we decide to move our eyes, the motor cortex sends signal to eye and a copy to the comparator

sound is…

mechanical energy: pressure waves (molecules pushing against one another)

compression

particles are close together