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Outline Human Visual Information Processing – cont.

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Presentation on theme: "Outline Human Visual Information Processing – cont."— Presentation transcript:

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

2 Visual Pathway 7/17/2019 COP4610

3 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

4 Retinal Ganglion Cell Responses
7/17/2019 COP4610

5 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

6 Simple Cells in the Visual Cortex
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7 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

8 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

9 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

10 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

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

12 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

13 Contrast sensitivity function
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14 Single Channel or Multiple Channels
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15 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

16 Virtual Contours 7/17/2019 COP4610

17 Reconstruction of Visual Perception
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18 Reconstruction of Visual Perception
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19 Exercise #1 7/17/2019 COP4610

20 Answers to Exercise #1 7/17/2019 COP4610

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

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

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