Visual Learning Instructor: Arnold Glass

Visual Processing Millions of computations are performed on the light patterns that fall on the retina before we see images consciously. Much of what goes on in the brain during vision is unconscious (prior to awareness). Processing begins with Sensory Registration, as shown in the next slide.

The Sensory Registration Stage Thalamus Pulvinar nucleus Lateral geniculate nucleus Superior Colliculus Retina Ganglion cells bipolar cells photoreceptors Midbrain (eye movements) Optic tract divides into 3 paths: Cortex Parietal Primary visual

Visual Pathways As shown in the previous slide, after sensory registration the visual pathway divides into: The eye-movement pathway (superior collicus) How pathway for all other movements (parietal cortex) What pathway (occipital cortex) produces visual perception

Visual Pathways As shown in the previous slide, after sensory registration the visual pathway divides into: The eye-movement pathway (superior collicus) How pathway for all other movements (parietal cortex) Damage to how pathway causes visual apraxia. What pathway (occipital cortex)

Visual Perception (What Pathway) There are multiple levels of analysis of the visual input involving many levels of representation, as shown in the next slide.

Stages of Visual Perception Shape construction Compare with memory Select plausible surface representations Integrate into 3D object representation Feature analysis Texture segmentation Binocular representation Compute 3D representation Sensory Registration

Compute 3D representation One early step is the comparison of the disparities between the retinal images to construct a single 3D image. Another early step is combining features into textures that ultimately define forms.

Stages of Visual Perception Shape construction Compare with memory Select plausible surface representations Integrate into 3D object representation Feature analysis Texture segmentation Binocular representation Compute 3D representation Sensory Registration

Select 3D representation Often more than one 3D representation is consistent with the sensory input. In this case, each representation is compared with memory and the most plausible is selected. Since the visual system relies on memory to select a single probable 3D representation, learning affects perception.

Upright and Inverted Moonscape

Towers

Barns and huts

Face Recognition Both form features (Clinton-Gore Illusion, upside-down Thatcher comparison) and spatial features (rightside-up Thatcher comparison) are important.

Types of Visual Agnosia LGN of Thalamus Retina Occipital Cortex Surrounding Visual Cortex Mesial Temporal Subcortex Inability to access memory associative agnosia Inability to integrate Features apperceptive Agnosia or simultagnosia Recognition Top Down Perceptual Processing Bottom up Perceptual Processing