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54 Cards in this Set

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frame of reference

set of axes by which the position or placement of an object is described

allocentric frame of reference

specify object's location independent of the viewer




provide spatial and directional information in unambiguous terms




objects are represented only in relation to each other

egocentric frame of reference

specify object's location with respect to the viewer

visual egocenter

the reference point on our body for judging the directions of objects




midway between the two eyes

transverse plane

x-axis




upper-lower halves




roll

coronal plane

y-axis




front-back halves




pitch

median plane

z-axis




left-right halves




yaw

semicircular canals

stimulated by rotational body movements




vestibular apparatus

otoliths

stimulated by linear body movement




vestibular apparatus

perception of absolute depth

retinal image cannot encode depth




depth perception by visual cues

retinal image size

optical cue for judging absolute depth




if we are familiar with the object, we can easily deduce its distance based on the retinal image

ocular cues - accommodation

accommodating




by the thickness of the lens, the brain can deduce the object's distance




no ambiguity since accommodating is directly related to object distance




accommodative mechanism is more engaged or near objects, negligible contribution to distance perception

ocular cues - vergence

when changing gaze from distant to near objects, eyeballs converge




when changing gaze from near to distant objects, eyeballs diverge

vergence

the horizontal rotation of the eyeballs to fixate an object on the foveal region of the retina

convergence

rotate inward

divergence

rotate outward

accommodation

changing the lens




blur spot detected on retina if refractive state of eye is not matched for object distance




motor command issued from brainstem to ciliary muscle -> changes shape of crystalline lens -> copy of motor command is sent to higher centers of brain that deal with perceptual function

pictorial cues

monocular depth cue




based on stationary optical information contained in 2D pictures

occlusion

if one object covers another, relative depth holds that occluded object must lie behind/farther away than the occluding object




monocular depth cue




acquired skill (between 5-7 months)

relative size

distant objects cast smaller images and visa versa

texture gradient

difference in texture




provides a strong depth cue to the visual brain




coarse texture arises from near objects




finer texture is caused by distant objects

linear persepctive

objects become smaller as they recede

aerial perspective

distant objects viewed through the atmosphere appear fuzzy and washed out




image contrast decreases due to light scattering caused by the atmosphere

image blur

objects out of foveal view are blurry




the greater the blur, the greater the relative depth in relation to the object we are fixating on

kinetic depth

motion cues generated by the movement of objects in different depth panes




closer objects are perceived to move a greater distance than faraway objects

motion parallax

the change in an object's direction of movement caused by self-motion




objects located farther than the fixation point move in the same direction as the observer




objects located between the fixation point and the observer move in the opposite direction




potent cue for relative depth

optic flow

the relative movement of passing objects

accretion and deletion

appearance (accretion) or disappearance (deletion) of objects behind an edge




dynamic versions of occlusion

size-distance relationship

as object distance increases, there is a dramatic reduction in retinal image size

size constancy - basic aspects

not directly related to the size of the retinal image




we learn about the true physical size of objects through visual experience and use depth information to calibrate a mental impression




breaks down under extreme conditions

Emmert's law

perceived size of an afterimage depends on the distance at which it was projected




reason: we take into account the distance of the plane on which the afterimage is projected in arriving at a perceived size of the afterimage

moon illusion

the vivid appearance of a very large moon on the horizon compared with the smaller moon perceived when it is directly overhead




we believed the horizon is farther away than the sky overhead, so moon right above us seems smaller




in reality they are the same size

Ponzo illusion

misconception of relative distance




visual system makes size judgements based on the background information contained in the scene




an object that casts an identical retinal image but that is believed to lie farther away will be perceived to be larger

Ames room illusion

misperception of relative size




see diagram in notes

binocular summation

visual stimulation through both eyes triggers a greater neural activity than stimulation through just one eye

advantages of binocular vision

binocular summation




greater visual sensitivity




visual field is larger




depth perception is 10x more exact

binocular fusion

the combination by the visual brain of the two retinal images to produce a unified picture of the visual scene

stereopsis

the deconstruction of the relative depths of different objects in the visual field




responsible for the outstanding depth perception that occurs under binocular viewing conditions (availability of stereoscopic cues + brain's ability to decipher such cues to generate depth perception)

Wheatstone's stereogram

shows how the disparity of retinal images is responsible for the vivid perception of relative depth

Vieth-Muller circle

both eyes are fixated on an object at a particular distance, there exists a theoretical circle in space in which all objects situated in it produce optical images at analogous retinal points in the two eyes




theoretical horopter

horopter

the set of environmental points that produce an image an analogous retinal sites for a given fixated point




sum of points in space that produce analogous retinal images

corresponding retinal images

images that form at optically analogous points of the two eyes




their distances from the fovea are identical




use fovea as reference point




position of any given retinal image by measuring its distance (d) from the fovea




retina labeled in two halves: nasal (n) and temporal (t)

retinal disparity

the difference in the location of the binocular images (D= dt - dn)

crossed disparity

objects located in front of the horopter crease binocular images on non-corresponding retinal points such that dt > dn




further from the front of the horopter the object is, the greater the disparity between the two images

uncrossed disparity

objects located farther away than the horopter create binocular images on non-corresponding retina points such that dt < dn




the farther the object is behind the horopter, the greater the disparity between the two images

role of binocular neurons

objects in left visual field trigger neural activity in the right visual cortex (and vice versa)




binocular neurons first appear in area V1

disparity selectivity in the visual cortex

2 ganglion cells at corresponding retinal points feed into a particular binocular neuron in area V1 -> neuron is activated -> sends information to higher parts of the visual brain -> decodes the incoming firing as having originated from an object having the specific disparity condition that coincided with the ganglion cells that fired




forms the the fundamental basis by which we perceive relative depth




different binocular neurons in area V1 encode all three categories of retinal disparity

Panum's fusion area

the limited range of depth both in front of and behind the horopter in which objects are perceived as single or fused

diplopia

when an object is situated so far behind or so far in front of the horopter that the magnitude of the retinal disparity is outside the range covered by the visual system and double vision appears

midline stereopsis

normal stereoscopic depth perception occurs for objects located along the midline




due to integration of visual information between hemispheres occurs through corpus callosum

free fusion

willful crossing/uncrossing of eyes




produces a spatial offset in their retinal image locations

correspondence problem

arises from a matching uncertainty between image points in the retina




challenge for the visual system is to ensure that a particular object point stimulates the correct circuit so that its true depth, relative to other parts of the object can be captured correctly

random-dot stereograms

a stereogram constructed by randomly assigning black or white dots across the image

binocular rivalry

a phenomenon that arises when two eyes are presented with different images




reveals importance of the role of orientation in binocular correspondence




at any given time, only one orientation will be perceived, and only briefly--after which the other orientation takes over, creating an oscillation in visual perception between the two orientations