Outline Human Visual Information Processing – cont.

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Presentation transcript:

Outline Human Visual Information Processing – cont. Models of some visual processing stages

Visual Pathway 7/17/2019 COP4610

How to understand the visual perception Neurophysiology Recording of cell responses Functional MRI Psychophysics Determination of the relationship between the magnitude of a sensation and the magnitude of the stimulus that gave rise to the that perceptual sensation 7/17/2019 COP4610

Retinal Ganglion Cell Responses 7/17/2019 COP4610

Retinal Ganglion Receptive Fields Has a circular center-surround organization Two major classes On-center Off-center How do they respond to a small spot of light? 7/17/2019 COP4610

Simple Cells in the Visual Cortex 7/17/2019 COP4610

Simple Cells rectangular shaped receptive fields segregated ON and OFF zones respond to a bright or dark bar represent a restricted region in the visual field respond best to a specific orientation non-optimally oriented stimuli will be ineffective in stimulating the neuron 7/17/2019 COP4610

Complex Cells larger receptive field than simple cells orientation tuned ON and OFF zones are mixed in the receptive field respond well to a moving bar direction selective 7/17/2019 COP4610

Hyper-complex Cells receptive field is selective for the length of the stimulus similar to complex cell receptive fields (orientation and direction selective) selective for features of shape such as length and width of the bar of light. 7/17/2019 COP4610

Visual Perception Modern view is that visual transformation is a creative process Vision transforms light stimuli on the retina into mental constructs of a stable 3D world Visual perception is a 3D percept of the world that is invariant to a wide range of changes in illumination, size, shape, and brightness of the image 7/17/2019 COP4610

Adaptation Adaptation Prior exposure affects the perception of brightness 7/17/2019 COP4610

Web’s Law The difference threshold is not constant The difference threshold changes as a function of the magnitude of the standard stimulus 7/17/2019 COP4610

Contrast sensitivity function 7/17/2019 COP4610

Single Channel or Multiple Channels 7/17/2019 COP4610

Neural Spatial Frequency Channels Neural receptive fields are tuned to the spatial frequency of the stimulus There seems to be a range of neural spatial frequency channels, each tuned to a different spatial frequency A spatial frequency channel can be adapted 7/17/2019 COP4610

Virtual Contours 7/17/2019 COP4610

Reconstruction of Visual Perception 7/17/2019 COP4610

Reconstruction of Visual Perception 7/17/2019 COP4610

Exercise #1 7/17/2019 COP4610

Answers to Exercise #1 7/17/2019 COP4610

Answers to Exercise #1 – cont. 7/17/2019 COP4610

Answers to Exercise #1 – cont. Paolina Borghese by Antonio Canova (1757-1822) - Galleria Borghese, Rome 7/17/2019 COP4610