Perception Flashcards

Question

What is the aim of visual perception?

Answer 1

Visual perception is about transforming the patterns of light that enters our eyes into some kind of representation of the world that helps us recognize and interact with the objects and people around us

Answer 2

Break up world into little pieces (such as colour and motion) Put it back together

Answer 3

FFA → Fusiform Face Area - Responds to faces more than other objects PPA → Parahippocampal Place Area - responds preferentially to places, such as pictures of houses EBA → Extrastriate Body Area → Specifically involved in the perception of body parts

Answer 4

Grandmother cell hypothesis - single-cell for each recognition (e.g. particular cell that recognizes your grandmother)

Answer 5

The ‘where’ system, binocular information Visual control of movement (milner and goodale, 1995) Egocentric Unconscious

Answer 6

The ‘what’ system Identification of objects and events Allocentric Conscious

Answer 7

Optic ataxia (damage to dorsal stream) No difficulty identifying visual stimuli Difficulty moving towards target More difficulty in pointing without delay (‘immediate’) It results from optic ataxia from lesions to posterior-superior parietal cortex: mis reaching (c), hand posture problems(b) and normal subject (a) If you have optic ataxia - can say what angle your hand should go but cannot actually do it

Answer 8

Visual agnosia (Patient DF - Milner & Goodale, 1995) - Damage to ventral stream Incapable of recognising faces, objects, shapes and sizes Capable of drawing from memory Incapable of copying picture of recognising own drawing Patient DF = damage on ventral stream Negotiates obstacles during locomotion Poorly estimates height of obstacles (verbal response) Highly proficient at grasping - appropriate hand orientation and grip aperture Evidence from healthy participants - shows difference between recognition and action Couldn’t hold letter in right orientation but when doing the action of the task it works Health PPT are offered a stimulus Verbal response (judging distance, size) Motor Response (point, reach and grasp)

Answer 9

See lecture notes for image (two same size dots in middle of large dots and middle of small dots) Verbal response more influenced by the illusion than motor response (Aglioti et al. 1995) As your aperture (finger distance) stays the same for both circles even though you perceive them as different sizes verbally Need to consider both streams in experimental designs

Answer 10

Our perceptual system = Evolved to reconstruct reality in a way that is biologically useful (e.g. to construct colour - bats echolocation may be coloured in their perception) Often learn most about how complex system works by studying situations where it makes mistakes

Answer 11

Change blindness is a phenomenon of visual perception that occurs when a stimulus undergoes a change without this being noticed by its observer Shows there are remarkable gaps in our perception Masking an image means we are less likely to notice a change Our interpretation of the visual field = Much sparser than subjective experience of “seeing” suggests Cannot process everything that is projected onto the retina e.g. Simon and Levin study at a college

Answer 12

William James (1890) → It is the taking possession by the mind, one out of several possible objects or trains of thought. Focalization, concentration, and consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others It is used and referred to many different kinds of mechanisms

Answer 13

External → Attending to stimuli in the world Internal → Attending to one line of thought over another or selecting one response over another Overt → Directing a sense organ toward a stimulus, like pointing your eyes of turning your head Covert → Attending without giving an outward sign you are doing so Divided → Splitting attention between two different stimuli Sustained → Continuously monitoring some stimulus

Answer 14

The selection of some visual stimulus or set of visual stimuli at the expense of others for further visual and cognitive analysis and often for the control of behaviour

Answer 15

Space based model vs object based Object based is more common

Answer 16

Attention is like a spotlight - moves about and allows us to selectively attend to parts of the visual world A model of visual attention that likens the focus of attention to a spotlight. Information outside of the spotlight is presumed not to receive processing that requires attention. Posner (1980) → Enhanced processing/detection occurs within this ‘spotlight’ Attention is directed towards ‘space’ according to spotlight model - then star shown - reaction time measured to see that curing attention to particular area of space reduces response time compared to when an alternative space is cued

Answer 17

Posner (1978), Posner (1980), Posner, Davidson & Snyder (1980) examined the effect of visually precueing regions of space on detecting the presence of a potential target Wanted to know if causing a shift of attention to a specific location in space improved processing of the subsequent stimulus Examined covert shifts of attention No eye-movements were allowed

Answer 18

Attention appears to be object-based, not location based E.g. image of house and other object overlaid but only details of one recalled - don’t pay attention to everything in the same place

Answer 19

Attended region can grow or shrink depending on the size of the area to be processed (Eriksen and Yeh, 1985)

Answer 20

Feature search → Target defined by the presence of a single feature Conjunction search → Target defined by the conjunction(co-occurrence) of two or more features Spatial configuration search → The target and distractors contain the same basic features

Answer 21

Efficiency of visual search is the average increase in RT for each item added to the display Measured in terms of search slope of ms/item Larger the search slop (more ms/item), the less efficient the search Some searches are efficient and have small slopes Some searchers are inefficient and have large slopes More distractors = More inefficient Faster to find the target than identifying that there is no target

Answer 22

he challenge of tying different attributes of visual stimuli, which are handled by different brain circuits, to the appropriate object so we perceive a unified object E.g. a vertical red bar moving to the right Colour, motion and orientation are represented by separate neurons How do we combine these features when perceiving the bar? Example of conjunction search with binding problem

Answer 23

Treisman and Gelade (1980) - Theory of visual attention Limited set of basic features can be processed in parallel preattentively but other properties (including correct binding of features to objects) require attention Preattentive stage → Processing of a stimulus that occurs before selective attention is deployed to that stimulus

Answer 24

Yes Illusory conjunction → An erroneous combination of two features in a visual scene E.g. Seeing a red X when the display contains red letters and Xs but no read Xs Illusory conjunctions provide evidence that some features are represented independently and must be correctly bound together with attention

Answer 25

Using own knowledge (top-down) Someone else directing attention (bottom-up)

Answer 26

Possible that objects can be attended to covertly (Poser, 1980) Can process information to some extent even when our eyes are not directly focused on it Looking out of the corner your eye Such strategies are of limited relevance during purposeful action such as making a cup of tea/crossing the road (Land, 2009)

Answer 27

When we inspect visual stimuli or scenes, what controls the movement of attention? Is attention captured by stimuli/objects or do we intentionally deploy attention? - sense fixation bias Is attention controlled by us or by the stimuli? - Attention is grabbed by what is salient Top-down processes versus bottom-up processes

Answer 28

Important information may not be salient - e.g. stop signs in a cluttered environment Salient information may not be important Doesn’t account for many observed fixations - especially in natural behaviour (Land)

Answer 29

Place the image of the object of interest on the part of the retina with highest acuity (the fovea) Keep image in eye stationary despite movement of the object or movements of ones head

Answer 30

The human eyes voluntarily fixate on those elements of a visual scene that carry essential and useful information The more information is contained in an element, the longer the eyes stay on it Yarbus (original experiments) - Saccadic eye movements reflect cognitive processes The distribution of fixations on the elements of a scene changes depends on the purpose of the observer People who think differently also, to some extent, see differently Where we look drive by top down processes (e.g. certain goal to find something in an image)

Answer 31

In cases where the task structure is evidence = More easily interpreted as it provides external referent to internal computations Eyes are positioned at the point which is not the most visually salient (most visually noticeable) but best for spatio-temporal demands of task Fixations are tightly linked in time to evolution of the task

Answer 32

In cases where the task structure is evidence = More easily interpreted as it provides external referent to internal computations Eyes are positioned at the point which is not the most visually salient (most visually noticeable) but best for spatio-temporal demands of task Fixations are tightly linked in time to evolution of the task

Answer 33

Expert vs Novice cricketers - See if fixation on ball predicts move Too fast for continuous smooth pursuit Cognitive capabilities between people differ - so differences in gaze behaviour Eye movements are predictive Better batsmen fixate on the bounce point earlier Shift eye movement attention (saccade) Expert pick up information faster to make a decision on where to hit the ball compared to a novice Novices less accurate Saccades (rapid eye movement for orienting gaze) are often made to a location in a scene in advance of an expected event Saccades were always preceded by a fixation on the ball as it left the bowler’s hand, showing that batsmen use current sensory data in combination with learnt models of the ball’s motion to predict the location of the bounce Thus, eye movement patterns appear to be shaped by learnt internal models of the dynamic properties of the world.

Answer 34

Eye movements driven by prospect of reward Cell responses reflect the reward of making a certain movement The mental programs that drive gaze selection are increasingly seen to be reward-based This direction is spurred by extensive neural recordings that show vast areas of the brain’s gaze computation system exhibit sensitivity to reward signals, as well as developments in reinforcement learning theory that make very specific predictions

Answer 35

Photoreceptors Ganglion Cells LGN Primary visual cortex Other cortical brain areas Mid-brain Brain stem Muscles Round trip from eye to brain to muscles takes a minimum of 200 msec. Cricket ball only takes about 600 msec. Prediction gets around the problem of sensory delays

Answer 36

Organisms adapt to their natural environment, it is important that experimental stimuli are sampled from the organism’s natural environment Visual search: Search for arbitrary objects is not very efficient Scene-based guidance would help you find the tap in the next scene (picture of kitchen) In real-world searches, real world guides visual search Scene-based guidance → Information in our understanding of scenes that help us find specific objects in scenes For instance, a mug or bowl is typically found on horizontal surface and a picture will typically be found on a vertical surface

Answer 37

Advocates the studying of behaviour under realistic conditions Originally applied to study of animal behaviour

Answer 38

Processes that subserve cognition are invariant and regular across conditions (e.g. size-weight illusion) Situational variability can be reduced or eliminated without affecting the nature of the process being measured

Answer 39

2d Limited resolution Size of display Unnatural responses Constrained head movements

Answer 40

Savelsbergh et al. (2005) investigated gaze behaviour of goalkeepers during a video simulation of a penalty kick They incorrectly assumed that the behaviours observed during the simulation were invariant and therefore representative of real-world behaviour Dicks et al. (2010) replicated Savelsbergh et al.’s (2005) study but with the inclusion of a real-world condition Dicks et al. (2010) observed similar behaviour in the simulation condition to that reported by Savelsbergh et al. (2005). The simulated condition created an artificially high percentage of fixations towards the legs of the penalty taker whereas in the real world the goalkeepers fixated almost exclusively on the ball.