Agenda

Pomona College Upcoming talks LCS 11: Cognitive Science Lorraine Tyler Thursday at 4:15PM, Edmunds 101 Vision William Marslen-Wilson Friday at noon, Edmunds 101 The eye and the HoUman’s visual rules Jesse A. Harris GQ 5.1 due Sunday, 9PM April 17, 2013 Signup for group meetings

Jesse A. Harris: LCS 11: Cognitive Science, Vision 1 Jesse A. Harris: LCS 11: Cognitive Science, Vision 2

The problem But this problem is nothing compared to . . . Vision feels easy, but it’s not at all. The miracle of vision! The visual system transforms a fragmented 2D image into a Constraints on vision coherent 3D construct. 1. Limited perceptual Veld 2. Physical blindspots 3. Subject to all kinds of illusions and perceptual error Miracle starts with the eye itself . . .

Jesse A. Harris: LCS 11: Cognitive Science, Vision 3 Jesse A. Harris: LCS 11: Cognitive Science, Vision 4 Visible eye

Cornea Curved transparent lens through which light enters. Focuses light onto the . Light bent and slowed by cornea. Iris Provides an adjustable aperture (colored part of eye). Hole in middle of iris, adjusts for amount of light Smaller when more light, limiting the amount let through to another lens.

Jesse A. Harris: LCS 11: Cognitive Science, Vision 5 Jesse A. Harris: LCS 11: Cognitive Science, Vision 6

Inner eye

Lens Contracts to give give more refractive power, needed for focusing on close objects. Power to accommodate by contraction decreases with age. Retina Light sensitive layer lining back of eye, containing multiple types of photoreceptors (rods and cones) and a chain of cells that provide the Vrst, rough processing, ending in the retinal ganglion cells. Fovea Area with dense population of cones for acuity

Jesse A. Harris: LCS 11: Cognitive Science, Vision 7 Jesse A. Harris: LCS 11: Cognitive Science, Vision 8 Age related decline Lens

Contraction Lens contracts to focus image on fovea when images are close (a).

Correction When the muscles cannot contract the lens enough (b), corrective lenses allow for adjustment (c).

Jesse A. Harris: LCS 11: Cognitive Science, Vision 9

Image projection Image projection

Psychologist G. M. Stratton wore lens over his eyes that inverted the images - to right side up. After about 8 days, adjusted well (but not entirely) to the inverted image.

G. M. Stratton (1865–1957)

Jesse A. Harris: LCS 11: Cognitive Science, Vision 12 Neural retina Neural retina

LGN Retinotopic maps

I Light gathered from retina maintains its spatial features of its representation in other areas of the brain 1. Signals sent from retinal ganglion cells to lateral geniculate nucleus (LGN) I Simplistic representation of how information is relayed from retina to the primary Cells in LGN responsible for retinotopic mapping - arrangement of receptive Veld according to an orderly 1. Light activates electrical impluses in retina 2. Carried via Vbers of the to highly speciVc map. areas in the lateral geniculate nucleus (LGN) 3. Transmitted to primary visual cortex (V1) in occipital region (back) of the brain

Jesse A. Harris: LCS 11: Cognitive Science, Vision 15 Jesse A. Harris: LCS 11: Cognitive Science, Vision 16 Stereopsis Random dot stereogram Stereopsis The perception of depth that occurs with normal, binocular vision.

I Slightly diUerent visual inputs to each eye due to diUerent locations

I Gives rise to depth perception

I Also to 3D movies

I 10% of population do not perceive depth in 3D movies, often due to damage to eye during development

Jesse A. Harris: LCS 11: Cognitive Science, Vision 17 Jesse A. Harris: LCS 11: Cognitive Science, Vision 18

Random dot stereogram Primary visual area

After basic processing, signals sent to V1 for

Selectivity Cells in V1 tuned to respond to very selective features

I orientation

I edges

I light

Classical Hubel & Wiesel demonstration of selectivity in V1: http://www.youtube.com/watch?v=IOHayh06LJ4

Jesse A. Harris: LCS 11: Cognitive Science, Vision 19 Jesse A. Harris: LCS 11: Cognitive Science, Vision 20 Fundamental problem of vision The image at the eye has countless possible interpretations.

I Visual input can matched up in any number of ways with the world

I Visual system applies rules and defaults to transform ambiguous or indeterminate cues into a coherent percept (mental construction what is perceived).

Jesse A. Harris: LCS 11: Cognitive Science, Vision 21

Rotated tables

http://www.michaelbach.de/ot/sze_shepardTables/Q

Jesse A. Harris: LCS 11: Cognitive Science, Vision 24 Construction of percept Rules Rule of generic view Construct only those visual worlds for which the image is stable (i.e., generic) view. The fundamental role of visual rules You construct visual worlds from ambiguous images in Rule 1 conformance to visual rules. Constants in construction implies Always interpret a straight line in an image as a straight line constants among visual interpretation - rules. in 3D.

Jesse A. Harris: LCS 11: Cognitive Science, Vision 25 Jesse A. Harris: LCS 11: Cognitive Science, Vision 26

Rules Rules Rule of generic view Rule of generic view Construct only those visual worlds for which the image is Construct only those visual worlds for which the image is stable (i.e., generic) view. stable (i.e., generic) view.

Rule 2 Rule 2 If the tips of two lines coincide in an image, then always If the tips of two lines coincide in an image, then always interpret them as coinciding in 3D. interpret them as coinciding in 3D.

Jesse A. Harris: LCS 11: Cognitive Science, Vision 27 Jesse A. Harris: LCS 11: Cognitive Science, Vision 28 Penrose triangle Penrose triangle

East Perth, Australia

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Kopfermann Vgure

Rules 1 and 2 allow us to prune many possible interpretations

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