the role of the cortex in visual perception

hierarchical model of visual processing

moving inward from the eye, each level of the visual system works by combining inputs from the level before it to create  increasingly complex representations

fragmented visual processing

distinct regions are specialized for specific aspects of vision. No one area processes the totality of visual perception

What is meant by the primary visual cortex (V1) being a map of the visible world covered by the two eyes? 

a given part of the visual field will always be processed by the same part of V, nearby parts of the visual field are processed by nearby parts of V1

simple cells

respond to bars of a certain orientation in the narrow, linear region of the visual fields preferred by a given cell. each will respond to either a light or a dark bar, but not both

complex cells

thought to receive inputs from multiple simple cells and thus sum their activity

what can cause agnosia?

can be caused by destruction of V1 and/or its inputs

• acquired deficit in perception often stemming from brain damage

What kind of connections does the primary visual cortex have with the non-primary visual cortex?

there are reciprocal connections between V1 (primary) and V2 (non-primary)

Describe the split off from V2 that occurs for dorsal and ventral streams. 

• dorsal: V2 V5 posterior parietal lobe (‘where’, visuospatial processing related to the control of motion)

• ventral: V2 V4 inferior temporal lobe (‘what’, recognition of visual stimuli)

What is the MT primarily concerned with? If damage is incurred, what happens?

Visual Motion, damage can occur to MT and cause Akinetopsia, where someone is unable to process visual motion 

elaborate on the role of the posterior parietal lobe

Contains a number of sub-regions with neurons that respond to the sensory properties of objects or to motor acts in which the subject (usually a monkey) interacts with an object. Highly connected to motor cortices, thought to be crucial for integrating vision into the control of motion

what is the V4 thought to integrate?

Information from earlier stages of visual processing to represent the basic features of objects that allow them to stand out from the background

list the three primary areas in the inferior temporal lobe that are tuned for specific kinds of visual stimuli

• parahippocampal place area (PPA)

• fusiform face area (FFA)

• prosopagnosia

parahippocampal place area (PPA)

responds to scenes consisting of multiple objects (landscapes, rooms)

fusiform face area (FFA)

responds preferentially to faces and similar stimuli

prosopagnosia

an inability to recognize familiar faces, which can be caused by damage to FFA

how does capgras syndrome occur?

injury to the ventral stream, damage to connection between visual and limbic regions (amygdala aka emotion) will cause a loss in emotional reaction to the sight of a particular person

law of specific nerve energies

parts in the nervous system are activated in a way that also influences your perception of the stimuli

• patterns of action potentials will be perceived as a visual stimulus if they occur in the optic nerve

• simple-single light stimulus can evoke different patterns of action potential from each ganglion cell

• perception is inferential, brain perceives based on periphery

• perception involves both bottom-up (info going from receptor to cortex) and top-down (info going from cortex to thalamus) processes