Cognitive PsychologyPSYC231

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

Comparing “greeble” recognition between novices and experts

Perceptual Organisation

• Gestalt laws:

– Simplicity (Closure)– Similarity– Good continuation– Proximity– Common fate– Familiarity

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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 formachine vision:

Maximal interpretationfrom minimal information