WEEK 2- SIZE CONSTANCY Flashcards
What factors are ignored when we are achieving visual object constancy
size, position, lighting, colour (though in extreme cases these changes have an effect like massive stimuli, objects in the periphery, silhouettes, fruit)
what factors are more costly to object processing?
plane rotation, depth rotation
when can object constancy fail
in cases of brain damage or stroke
what terms can be used to refer to size in the world?
objective/ physical/ linear
what terms can be used to refer to subjective/ introspective size?
apparent/ perceived
what terms can be used to refer to size related to visual angle in the retinal input or o a projected surface like a mirrror window or thin frame ?
projected, proximal, angular, retinal
what are the arguments for whether we percieve the objective world or our projected input or neither
Gibson and Epstein argued for constancy in normal visual experience and said we can only access input projections by paying special attention. Rock argued that our intial percepts are closer to the projected stimulus
what did Hatfield 2012 argue?
said both the objective world and the projected stimulus are accessible to us and we can show this by careful use of instructions
what happens every time you double the distance of an object to the eye?
the retinal angle at your eye shrinks in half
what did Granrud and colleages investigate?
how size estimates change during a child’s development and the influence of distance on outdoor size estimates. they developed a metacognitive account of how we perceive object size
what is the Ames room
depth cues lead us to misperceive distance and this causes us to misestimate the objective size of one of the people being much smaller
what did Granrud claim about near distances?
even young children can estimate objective size quite accurately at distances up to 3. at near distances multiple depth cues eg accomodation, ocular convergence, binocular disparity, and motion parallax give accurate information about objective distance to an object. so do not need to use explicit distance compensation metacognitive strategies
what are size estimates like for intermediate distances (-6m)?
both children and adults are fairly accurate but they underestimate objective size slightly
what are size estimates like for greater distances (>15m up to at least 60m)
children under 10 years greatly underestimate the objective size of objects whereas older children and adults show nearly accurate size constancy.
what causes children to improve estimations of the objective size of distant objects?
Ho1- perceptual learning- children slowly learn to use visual cues (leibowitz, 1974 size distance invariance hypothesis). Ho2- metacognitive theory children learn to explicitly use a cognitive strategy of compensating for size changes with distance. without this strategy they greatly underestimate size for distances beyond 10m.
what does the size distance invariance hypothesis state
this claims that our visual system estimates the distance of an object then determines the objects objective, physical size based on its angular projected size on our retina, ie perceived distance causes our perception of size
what does Granrud argue about perceptual versus cognitive factors in size estimation
He claims that there is no developmental change in how distant objects appear to us. adults have learnt to estimate the objective size of objects accurately whatever the distance of the object by using explicit metacognitive strategies. these strategies compensate for objects looking smaller when they are further away
what skills let us estimate objective size?
merriman, moore and granrud 2010- children were asked which comparison disc had the same objective, physical size as the target disc at 61m or at 6m. children with better verbal and visuospatial reasoning skills were more accurate suggesting that these skills underlie metacognitive strategy use- and these verbal and visuospatial reasoning skills develop with age
what granrud 2009 study suggested that a metacognitive strategy is used to estimate object size at far distances?
children who could explain how distance affects image size usually were 1) quite accurate at estimating the objective size of objects 61 away and 2) often explicitly reported using a distance compensation strategy ‘i know if you go far it’s gonna look smaller’ so it will look like one of those [points at a small comparsion disc] but know it’s really one of these bigger ones. children who did not seem to fully understand how distance affects image size usually 1) underestimated the size of objects 61m away, and 2) did not report using a strategy. by 5 years most children roughly know how distance affects aparent size but it often takes years more for them to learn how to accurately apply this knowledge so they can explicitly use a distance compensation strategy.
what instructions were given to participants in granruds 2009 study to test when children use a metacognitive strategy?
apparent size: choose a comparison object that matches the size that the test object appears to be. objective size: choose a comparison object that matches the test object’s actual size regardless of it’s apparent size. given these instructions for near AND far object
what were the results of the granrud 2009 study?
older children are more likely to use a metacognitive strategy but it is strategy use (not simply age) that seems to predict whether objective size is underestimated at far (61m) distances
why does undercompensation occur when estimating objective size at far distances?
likely occurs because young children respond based on how the object looks and they do not use an appropriate metacognitive strategy.. note this underestimation is typically only 20-30 per cent
how do some adults and older children accurately estimate objective size at far distances?
because they know that distant objects look smaller than they are
why do some overcompensate when estimating objective size at far distances?
seems a clear marker of the use of a poor metacognitive compensation strategy since visual cues rarely suggest that a distant object is larger than it really is
what happens to size estimation during development?
pre 5 years- start to learn visual cues to depth. by 5 years- explicitly know things look smaller when further away (essential for further distances). 5-10 years- gain verbal and visuospatial reasoning skills. by 11 years- have acquired an explicit metacognitive strategy (get to adult levels of size estimation for FAR distances)
how do we estimate the PROJECTED size of objects on windows and mirrors?
perceived size seems to be a compromise between obejective, physical size and projected retinal size (koh & charman 1999) with an unrestricted field of view and good, rich cues to depth, size estimates using a mirror are close to those based on size constancy so they are near to an objects objective size even if it is unfamiliar. however size estimates are increasingly based on projected angular size on the reinta as depth cues are removed- so we underestimate objective size. despite this use of projected size people cannot estimate accurately the size of projections of objects on the surface of mirrors and windows .. they only seem to have explicit access to perceived size
what is the train window illusion
for both mirrors and windows the PROJECTED extent on the glass surface is exactly half the physical extent of the target object IF the target object is the same distance from glass as the observer. and for the mirror if the target object is your own face or body this (same distance) is always the case.
what was the Lawson and Bertamini 2006 size- estimation task?
participants stood facing a mirror. they had a set of 15 ellipses and were told that the ellipses varied in size form 7cm to 28 cm long. on some trials they had to select the smallest ellipse which would, if it were placed directly on the surface of the mirror just cover up their face, so that they would no longer see the reflection of their face in the mirror. on the other control trials they had to choose the ellipse that would match the size of a test ellipse. they were not allowed to place ellipses on the mirror. instead they were told to hold up one ellipse at a time against the wall to the side of the mirror. they could pick as many ellipses as they wished and could re-select ellipses before making a decision
what were the results of the lawson and bertamini 2006 size estimation task
overestimation occured even after people were told to use a useful strategy.. so it is not surprising that few people are aware of the size or position of reflections despite their everyday interactions with mirrors. but maybe faces are special stimuli? conclusion: people cannot perceive the size of projections
what does granrud say about why at near and intermediate distances we are unaware of the discrepancy between perceived and objective size why does this break down at further distance? how come things start to look smaller?
granrud argues its because distance perception starts to break down so objects at 60m seem nearer than they really are, because of this objects apparent size is too small.. this in turn means we need an explicit cognitive strategy to compensate. if granrud is correct this predicts that when we are relying on depth information to infer size then if depth cues are reduced (eg if we look up at an airplane) we should make larger underestimation errors so such objects should look especially tiny.. there is some evidence for this.
