Understanding Visual Processing: Pathways, Middle Vision, and Object Recognition - Prof. M, Study notes of Cognitive Psychology

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Perceiving and

Recognizing Objects

Introduction

• (^) How do we recognize objects?  (^) Retinal ganglion cells and LGN = Spots  (^) Primary visual cortex = Bars
• (^) How do spots and bars get turned into objects and surfaces?  (^) Clearly our brains are doing something pretty sophisticated beyond V

Figure 4.2 The main visual areas of the macaque monkey cortex

Figure 4.3 A partial “wiring” diagram for the main visual areas of the brain

What and Where Pathways

• (^) The same visual input occurs in both ( a ) and ( b ) and a V1 neuron would respond equally to both. A V2 neuron might respond more to ( a ) than ( b ) because the black edge is owned by the square in ( a ) but not in ( b )

What and Where Pathways

• (^) Inferotemporal (IT) cortex: Part of the cerebral cortex in the lower portion of the temporal lobe, important for object recognition  (^) Part of the “what” pathway
• (^) Lesion: In neuropsychology:  (^) 1. ( n ) A region of damaged brain  (^) 2. ( v ) To destroy a section of the brain
• (^) When IT cortex is lesioned, it leads to agnosias  (^) Agnosia: Failure to recognize objects in spite of the ability to see them

Figure 4.5 Cells in the inferotemporal cortex of macaque monkeys are interested in specific stimuli

What and Where Pathways

• (^) Grandmother cells  (^) Could a single neuron be responsible for recognizing your grandmother?
• (^) Feed-forward process: A process that carries out a computation one neural step after another, without need for feedback from a later stage to an earlier stage  (^) Object recognition occurs so quickly that feed- forward processes must be occurring

What and Where Pathways

• (^) Object recognition is fast!  (^) Studies indicate that object recognition happens in as little as 150 ms  (^) This is such a short time that there cannot be a lot of feedback from higher brain areas  Feed-forward process: Carries out a computation (e.g., object recognition) one neural step after another, without need for feedback from a later stage to an earlier one

The Problems of Perceiving and Recognizing Objects

• (^) What do you see?

The Problems of Perceiving and Recognizing Objects

• (^) What do you see?

The Problems of Perceiving and Recognizing Objects

• (^) Is this the same red house that was shown before?

Middle Vision

• (^) Middle vision: A loosely defined stage of visual processing that comes after basic features have been extracted from the image and before object recognition and scene understanding  (^) Involves the perception of edges and surfaces  (^) Determines which regions of an image should be grouped together into objects

Middle Vision

• (^) Finding edges  (^) How do you find the edges of objects?  (^) Cells in primary visual cortex have small receptive fields.  (^) How do you know which edges go together and which ones don’t?