Perceptual Theory “Touch teaches vision” Gestalt principles

Depth perception is a particularly thorny problem: We “see” objects as having three dimensions & as nearer/farther from us. But how do we do this, since our retinal image is not 3-d? Proposed empiricist solution from Bishop Berkeley: “Touch teaches vision.” That is, the empiricists agreed that something had to be veridical, or else we wouldn’t have a starting point to calibrate the other sensory information. So they decided that touch must be inherently correct from birth, and thus vision could “learn” from touch that things have three dimensions. Hence, the nativist – empiricist debate.... – dropped babies – babies on visual cliffs – kittens bumping into table legs – kittens in carousels – monkeys raised in the dark, etc.

Theoretical perspectives & evidence Empiricist view: meaningful perception is learned Bishop Berkeley – “Touch teaches vision” British Empiricists/Associationists – “blank slate... assoc of sensations & ideas William James– infant’s world is “Blooming buzzing confusion” Blakemore & Cooper – kittens in vertical versus horizontal environments Held & Hein – kittens in carousel Nativist view: Some meaningful perception occurs innately Immanuel Kant [Time (before/after) & Space] Gibson & Walk – visual cliff (animals, humans) versus dropped babies Fantz – infant’s perceptual preferences – complexity, color, etc – faces! Cognitive view – perception is “constructed” via cognitive processes Gestalt psychology [“Gestalt Organizing Principles”] Richard Gregory [Illusions & ambiguous figures]

Nativist views: some aspects of visual experience are innately meaningful Additional meaning is acquired via maturation & learning Robert Fantz -- infants’ visual preferences Patterns, such as checkerboards with differing numbers of squares, vertical stripes of different thicknesses, and drawings of regular versus scrambled faces were shown to infants two at a time. Because of the placement of the infant in a testing chamber, the experimenter could actually see a reflection of the stimulus on the infants’ cornea. Fantz measured total looking time as an indicator of preference. Among Fantz’ findings were that infants tend to prefer patterned surfaces to uniform surfaces and complex patterns to simple patterns. Also, sharply contrasting colors, larger squares, and medium brightly lit objects were more appealing. Faces: infants (including newborns) preferred regular faces over scrambled faces. Immediately after birth in the delivery room, babies will not only fix on a drawing that resembles a human face but will follow it for 180° arcs, with eyes and head turning to keep it in view (Goren et al., 1975). A scrambled face does not get the same kind of attention, nor do infants follow the distorted face with their eyes or head.

Eleanor Gibson & Richard Walk: The visual cliff experiments regarding depth perception in infants

Empiricist views: “mind” starts with no visual experience, and thus must acquire the ability to have meaningful perceptions. J Locke: Mind = tabula rasa at birth Visual sensations have no meaning at birth (c.f., W James’ “Blooming buzzing confusion”) If so, then what provides us with information regarding what our visual sensations mean? Bishop Berkeley – “Touch teaches vision” British empiricists – More generally, repeated experiences with the environment, where pleasures, pains, etc occur in conjunction with visual experiences, provide us with the necessary information re: Meaning. In modern behavioral terms, we’d say that experiences via operant & classical conditioning & social/observational learning provide us with the relevant information.

Blakemore and Cooper – kittens in vertical versus horizontal environments Neurons in the visual cortex are orientation-specific, but usually are equally distributed around the 360 degrees of the visual array After being raised in constrained environments, distribution of neuron sensitivities tended to be limited to mostly horizontal or mostly vertical... However, upon being released into a “normal” environment, the kittens quickly acquired the ability to respond to all orientations...

Held & Hein Kittens were kept in the dark for a period of eight weeks from birth except for an hour per day when they were kept in a 'Kitten Carousel'. A device which let one cat move it while the other followed around but was not in control of the motion. This meant that both cats had the same visual experience. The immobile kittens were unable to blink and didn't stretch out their paws when lowered to the ground. However, when allowed free movement they quickly learned the ability, implying that the perception of depth is learned and related to the motor system.

Cognitive “constructivist” views: The mind constructs meanings, based on prior experiences, logic, problem solving, etc Sensory information is astoundingly skimpy compared to the richness & complexity of our subjective perceptual experiences. Since the sensory information is inadequate to account for those experiences, something about the mind must provide the additional richness. Richard Gregory – major champion of constructivist views, using experience of illusions & ambiguous figures as his primary evidence Illusions almost invariably arise from 2-D figures, wherein the viewer has the impression that there are 3 dimensions in the figure; or else from ambiguous pictorial figures, wherein the viewer sometimes sees one figure, other times a different figure. Since the images don’t change, the only possible explanation is that the “mind” must be manipulating the visual information, trying to make sense of it.

View from front of mask View from rear of mask View from rear, close-up “The effect of filming the inside of the mask is very strange. Although the face is impressed when looking inside, there are not visual cues as to exactly what you are looking at other than its a face, so it pops out at you, and looks unnervingly real. Even as it moves around in the restorers hands, and even though you know its impressed, the illusion persists.” -- Nik Williams Images from the restoration of the mummy of Hor

The Ponzo illusion – arises in context of linear perspective cue for depth

The Necker Cube

Fin Next lecture: Gestalt principles Examples Assignment for Tuesday, Feb 15