What is a retinotopic map and how is it created?

retinotopic map is An inverted topographic map of the object or scene being viewed with the eyes

Retinotopic map is distorted in the cortex

More space allocated to locations near the fovea

Fovea signals Accounts for 8-10% of retinotopic map in cortex

this distortion is known as cortical magnification

What methods are used for cortical mapping and how do they work??

PET MRI & fMRI scans are used in cortical mapping

Positron emission tomography

Person is injected with a harmless radioactive tracer

Tracer moves through bloodstream

Monitoring the radioactivity measures blood flow

Changes in blood flow show changes in brain activity

PET-subtraction method. Brain activity is determined by

Measuring activity in a control state

Measuring activity in a stimulation state

Subtract the control activity from the stimulation activity.

Remainder is stimulation from performing a specific task

Functional magnetic resonance imaging fMRI

Hemoglobin carries oxygen and contains a ferrous molecule that is magnetic

How is the visual cortex organized? Describe the functions of the organizations

The visual Cortex is organized in columns according to: Location, organization, ocular dominance

Location

Receptive fields at the same location on the retina are within a column

Orientation

Neurons within columns fire maximally to the same orientation of stimuli

Adjacent columns change preference in an ordely fashion (gradually)

1 millimeter across the cotex repesents the entire range of orientation

Ocular dominance

Neurons in the cortex respond preferentially to one eye

Neurons with the same preference are organized into columns

Degree of dominance 1=full dominance (left eye) 4 equally effective for both eyes 7= right eye dominance

Dominance changes systematically

What were the findings of Ungeleider and Mishkin’s study? What modification was made

showed that there are pathways in the visual cortex that separately transmit information regarding what is seen and what is located

They used the technique of Lesioning (utilizing monkeys)

Used object and landmark discrimination task

Found temporal lesion resulted in poor object discrimination

 Parietal lesion resulted in poor landmark discrimination

Concluded the ventral pathway (flows to bottom part of brain) is a “what” path and the dorsal pathway  (flows to top part of brain) is a  “where” path

When parietal lobe is damaged loss of judgments of location

When temporal lobe is damaged loss of object shape judgment

description of pathways leaves out feedback connections which are essential and likely responsible for top-down processing

Dorsal pathway actually a how pathway (where and an action) found by  Goodale and Milner

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Describe double-association and the experiment used to demonstrate it

Double-dissociation: two functions involve different mechanisms and operate independently

Ganel demonstrated a separation of perception and action in non-brain damage subjects

used illusory pattern which generates a distortion of perceived line length

Define cortical module. What regions of the brain are an example of a cortical module?

Cortical module: a brain structure that processes information about specific stimuli

Cortical modules for places (para-hippocampus place area PPA) and bodies (extra-striate body area EBA)

What is the cause of prosopagnosia?

Temporal lobe damage in humans results in prosopagnosia-inability to recognize faces

What are hypercolumns and what do they repsond to?

Hypercolumns Responds to specific locations on a retina and contain

A single location column

Left and right dominance columns

A complete set of orientation columns

Known as the ice-cube model