PS2111 CDL Lecture 2.pptx

PS2111 The visual guidance of action Carlo De Lillo George Davies Centre, Room 3.12 Email: [email protected] Assumptions of traditional approaches to visual perception Perception starts with static pattern of light intensity on the retina Retinal images are ambiguous (see stimulus equivalence problem) T...

PS2111 The visual guidance of action Carlo De Lillo George Davies Centre, Room 3.12 Email: [email protected] Assumptions of traditional approaches to visual perception Perception starts with static pattern of light intensity on the retina Retinal images are ambiguous (see stimulus equivalence problem) The outcome of perception is the formation of an internal representation of objects in the environment Our actions towards objects in the real world are informed by these internal representations However, we are capable of very rapid responding to visual input The work of J.J. Gibson (1966; 1979) Stimulation by light in itself does not lead to perception e.g. eyes covered with halves of table tennis balls Light energy is affected by the medium that it traverses e.g. water, glass, air different surfaces reflect light in different ways depending on their textures, opacity, slant etc. e.g. light reflected by polished or textured surfaces Structured light carries information visual perception occurs – e.g. light structured by texture information about distance about shape and general layout of objects in the environment isual cliff, E.J. Gibson (Gibson & Walk, 1960) Perception of depth from texture 6-14 months old infants variety of animal species glass textured surface textured surface apparatus Optic array pattern of light reaching a point in space determined by the nature of reflecting surfaces Optic flow changes in the pattern of light reaching a moving observer transformations of the pattern specify layout, shape and movement Structural invariants tterns of relationships that remain constant despite changes inal image e.g. a possible invariant specifying size constancy ratio of an object’s height to the distance between its base a the horizon horizon }{ a b } } a1 b1 Across all distances from the viewer, if a:b = a1: b1, then A and B are the same size Transformational invariants Flow - locomotion Non flow - stasis Outflow – approach – centre of outflow – direction – shift of the centre change of direction Inflow - retreat from Direct perception Optic array and the optic flow provide all the information needed for perception Role of the perceiver: – Pick-up information in optic array and optic flow – No need to process the retinal image and internal representations Perception is “direct” Affordances J.J Gibson proposed a radical theory of affordances the product of perception is not an internal representation organisms detect functional value of surfaces and objects bridge the gap between perception and action e.g. – a mail-box affords posting letters Micro-affordances (Ellis & Tucker, 2000) Potentiation of action components by seen objects Participants required to make a power or precision grip in response to a high or low pitch tone, respectively If an object presented in the background (irrelevant to the task) affords a grip compatible with the response, then response is faster and more accurate Response switch Tone Object presented Compatible – fast-accurate Not compatible – slow-more errors imilar results with wrist rotation in response to low and high pitch tones Neo-Gibsonians”: e.g. David Lee emphasis on the relationship between perception and action detection of invariants in the optic flow ecological contexts – locomotion – maintain posture – avoidance of obstacles Information needed to guide action Exteroceptive information from the environment e.g. spatial relationship between landmarks to guide navigation Proprioceptive information from the body e.g. maintain balance with eyes closed Exproprioceptive (Lee, 1977) position of the body relative to the environment e.g. obstacle avoidance Optomotor response (Kalmus, 1949; Blondeau & Heisemberg, 1982) fly walking on a platform a flying fruit fly compensates cylinder is turned for rotation of the environment along the fly turns in the same direction different axes optic flow of texture is minimised in a natural environment optic flow specifies movement of the insec (Gibson, 1966) The swinging room (Lee & Aronson, 1974; Lee & Lishman, 1975; Lishman & Lee, 1973) suspended bottomless box wallpaper provides texture movements of the room produce optic flow – expanding optic flow subject sways backwards – contracting optic flow subject sways forward visual information overrides proprioceptive information Toddlers (13-16 months) in the swinging room show the same behavioural pattern visual information overrides proprioceptive information early in development ime to contact void collision with obstacles traditional theories - calculate initial distance from objects depth cues etc. - calculate speed - divide distance by speed - computationally complex - possibility of errors from different sources ee (1976) all the information needed can be conveyed by only one variable if speed is constant tau = inverse of rate of expansion of retinal image eye surface textured surface Each element of texture moves from the point of fixation Behaviours that might be regulated by using time to contact long jumping (Lee et al., 1982) catching a bus jumping over puddles avoiding obstacles Fishing gannets (Lee and Reddish, 1981) originally posted to Flickr as JF100423_DSB_Puddle Jumper Author Derek Bridges Time to contact in fishing gannets (Lee and Reddish, 1981) dive from height of 30m reach speed of 24m/sec wings streamlined just before reaching the water predictions based on corrected tau values predictions based on height, velocity and acceleration observation of bird’s behaviour predictions based on tau fit the data Summary Ecological approach Link between perception and action Key concepts – Optic array – Optic flow – Invariants Radical theory of affordances Micro-affordances Tau Reading Essential Bruce, Vicki; Georgeson, Mark A ; Green, Patrick R 2003 Visual Perception: Physiology, Psychology and Ecology. Chapter 1, pp. 3-7; Chapter 10; Chapter 11, pp. 315-332; Chapter 12, pp. 348-358. Ellis, R.& Tucker M. (2000). Micro-affordance: the potentiation of components of action by seen objects. British Journal of Psychology, 91: 451-471. Available electronically via ingenta on line-library catalogue Additional Eysenck, M.W ; Keane, M. T. 2010 Cognitive Psychology: A Student's Handbook, 7th Edition. Chapter 4. Gordon, I. E. Theories of Visual Perception. Hove, Psychology Press, 2004. v. 3rd ed, Chapter 6.