Psych 261 Final

Where do axons from retinal ganglion cells generally project?

The CNS

Main target of retinal ganglion cells

LGN of the thalamus (for the geniculostriate pathway)

Where does the LGN of the thalamus send its info?

Primary visual cortex (striate cortex/V1)

What occurs in the PVC

Basic visual processing

Where does visual info go after reaching the PVC

The secondary visual cortex (V2)

How does the secondary visual cortex connect to the PVC

Bidirectional connections (travels ventrally & dorsally)

Purpose of V2

Continues basic visual processing

2 general pathways from which information is passed from early processing areas to other cortical areas

Dorsal stream & ventral stream

What is included in the dorsal stream

Superior & middle temporal cortex

What is included in the ventral stream

Inferior temporal cortex

What is the dorsal stream known as

The “where” pathway - Processing object movement & location + visually guided action

What is the ventral stream also known as

The “what pathway” - Processing object form & colour - heavily involved in object recognition

V4 role

Colour perception

Which pathway is the V4 involved in

Ventral (what) - colour/object form + object reco

Dmg to V4 leads to

Cerebral achromatospia

Cerebral achromatospia effect

Impaired colour perception (w/o any dmg to colour processing machinery in the retina)

When dmg extends to regions surrounding V4, it can result a complete loss of colour vision

Cells responsive to specific categories of stimuli include (w/i ventral)

Primarily further down the ventral visual processing stream (esp. the inf temp cortex)

Fusiform face area (particularly responsive to faces)

Parahippocampal place area (primarily responsive to places)

Certain regions also respond to inanimate vs animate

How do receptive fields change throughout the ventral visual stream

Inc in size & complexity as they get closer to the inferior temporal cortex

Difference b/w PVC & Inferior Temporal Cortex - what they respond to

Cells in the inferior temporal cortex respond to objects regardless of their retinal size or their orientation; thus unlike cells in the primary visual cortex, those in the inferior temporal cortex respond to the identify of objects, and not just to basic visual features.

Damages to parts of the ventral stream can lead to

Visual Agnosia

Visual agnosia

A deficit of visual object recognition

can recognize objects by touch or by sight; they’re just unable to recognize objects by vision alone.

Subtype of visual agnosia (1)

Apperceptive agnosia (or visual form agnosia)

Have problems even putting together the basic features of objects, and so they have trouble copying objects.

Subtype of visual agnosia (2)

Associative agnosia, can put the features of objects together, but are unable to link the resulting visual forms with meaning.

These patients can copy objects just fine, but even as they copy them, they cannot identify them.

Prosopagnosia

Problem w/ facial recognition.

Can make out the various features of a face, but they cannot put the features tgth

Damage to the dorsal stream can lead to a condition known as

Optic ataxia

Optic ataxia

a failure to point or reach accurately towards objects presented visually (primarily in the periphery)

can visually identify objects just fine

also don’t have an underlying motor problem; their problem is specific to visually guided reaching movements.

What areas of dorsal pathway are involved in processing visual motion perception

Middle-temporal cortex (MT or V5)

Medial superior temporal cortex (MST)

Both MT/V5 & MST have

Retinotopic maps (MST is less defined)

Size of receptive fields MT vs MST

MT - small receptive fields

MST - large receptive fields

What do the MT receptive fields code for?

MT: Movement direction, speeds for object movement, changes in object speeds, object movements relative to THEIR background (direction, speeds/changes, movements relative)

What do MST receptive fields code for?

Dorsal part - expansion/contraction and rotation of objects

Lateral part - object movement relative to THE background

Damage to motion processing areas can lead to condition known as

Akinetopsia

akinetopsia

characterized by a specific inability to visually perceive object motion.