Cognitive Psychology PSYC231 Perception 2 Dr. Jan Lauwereyns, EA619, ext. 5042

Prosopagnosia: Face blindness

Light falls on the retina, and is then processed through the visual system. But it only becomes meaningful through interpretation ‘in context’ Divide the environment in meaningful units Usually: Objects Organisation of visual information, in structures or patterns that we ‘know’ At a level of complexity that is relevant for our behaviour, for our goals and worries The “What" (Ventral) Stream: Object Recognition

Figure 3.9 (p. 63) A model for recognizing letters by analyzing their features. The stimulus, A, activates three feature-units. These feature-units cause strong activation of the A letter-unit and weaker activation of units for letters such as the N and the O, which lack some of A’s features. The A is identified by the high level of activation of the A letter-unit.

Figure 3.10 (p. 64) Different kinds of A’s that share features.

Feature Integration (simple to complex) Recognition by Components, RBC (Biederman) – Visual ‘alphabet’ – Infinite combinations – accommodates propositional descriptions – importance of ‘junction points’ – Viewpoint-independent

Figure 3.22 (p. 72) (a) A familiar object; (b) the same object seen from a viewpoint that obscures most of its geons and therefore makes it harder to recognize.

Can you read this?

The template-matching approach –E.g., bar codes –But requires infinite number, each template has to be learned as new, not robust against visual degradation –Matching to exemplars based on similarity –Viewpoint-dependent

Arcimbaldo

The Forest Has Eyes, Bev Doolittle

Are faces special? One of my favorites: the “greeble” study by Gauthier et al (1999, Nat. Neurosci.)

Comparing “greeble” recognition between novices and experts

Perceptual Organisation Gestalt laws: –Simplicity (Closure) –Similarity –Good continuation –Proximity –Common fate –Familiarity

a b c d e f g h i j k l n p o m q r s t

a b c d e f g h i j k l n p o m q r s t

Familiarity

Influence of context Objects are not presented in isolation Effects of visual context –E.g., 3D illusion Effects of semantic context –E.g., Effects of knowledge, expectation

Difficulties for machine vision: Maximal interpretation from minimal information