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Outline

Explore the models and stages of visual processing, including retinal ganglion cell responses, simple cells in the visual cortex, complex and hyper-complex cells, and the process of visual perception. Discover how the brain transforms light stimuli into a stable 3D percept of the world and learn about adaptation, Weber's law, contrast sensitivity, and neural spatial frequency channels.

jbalducci
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Outline

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Presentation Transcript

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

  2. Visual Pathway 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 COP4610

  4. Retinal Ganglion Cell Responses 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? COP4610

  6. Simple Cells in the Visual Cortex COP4610

  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 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 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. 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 COP4610

  11. Adaptation • Adaptation • Prior exposure affects the perception of brightness 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 COP4610

  13. Contrast sensitivity function COP4610

  14. Single Channel or Multiple Channels COP4610

  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 COP4610

  16. Virtual Contours COP4610

  17. Reconstruction of Visual Perception COP4610

  18. Reconstruction of Visual Perception COP4610

  19. Exercise #1 COP4610

  20. Answers to Exercise #1 COP4610

  21. Answers to Exercise #1 – cont. COP4610

  22. Answers to Exercise #1 – cont. • Paolina Borgheseby Antonio Canova (1757-1822) - Galleria Borghese, Rome COP4610

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