PYSC 370 association cortex

ventral stream

• temporal association cortex

• what are the objects

• uses shape, colour, touch, sound to identify objects

• important for semantic knowledge/memory

dorsal stream

• parietal association cortex

• where are the objects

• visual and somatosensory info used to understand spatial relations and guide attention and movement related to objects and space

convergence of sensory info

• visual and somatosensory info converge onto parietal association cortex to understand where object is w respect to u

• visual, somatosensory and auditory info converge onto temporal association cortex to identify object

divergence of sensory info

• visual info diverge onto temporal and parietal association cortices

• same visual info can be used for diff purposes

• same V1 signals/retinal inputs can be processed differently

categorical linking

• diff types of stimulus but understood as related

• horsey as wooden, real, carousal 

associative linking

• association between diff objects/events

• diff situations involving the stimulus

• horseback riding, horsey in barbie movie

image linking

object in diff orientation

object representation

• categorical linking

• associative linking

• signals from other modalities

• image linking

• emotional valence

inferotemporal cortex activity 

• represents higher order processing

• monkey presented with another monkey face: high firing rate

• control: components of face rearranged - lower increase in firing rate

• diff monkey face: still very high firing rate

• white bar on mouth: firing still high

• white bar on eyes: firing still high

• no color: relatively high firing rate

• man face: still high firing

• hand: no firing

• neurons specific to facial recognition 

diff RFs

• V1: 1 degree

• V4: 10 degrees

• Inferotemporal cortex: up to 100 degrees

hypercolumn

cluster of columns that represent a class of stimuli (type of object)

perceptual constancy

• ability to recognize an object despite variations in appearance

• achieved by population coding of viewpoint-specific neurons

• or convergence in even higher visual regions in frontal association cortex

associative learning

• allows neuronal representations to be linked

• before: when stimulus is shown, tent highly active but horse is not

• after: when stimulus is shown both somewhat in the middle and same firing = neurons are connected

• requires the MTL including the hippocampus = links neocortical representations

apperceptive agnosia

• damage to posterior inferotemporal cortex

• can’t put parts tgt

• unable to construct sensory representations of visual stimuli - can’t copy drawing

associative agnosia

• damage to anterior IT

• higher up in associative hierarchy

• cannot interpret, understand or assign meaning to objects

• can’t link the object to other things in the world

dorsal area of dorsal stream

• closer to somatosensory cortex

• motor functions related to space

ventral area of dorsal stream

• closer to visual cortex

• pure spatial functions in perception and cognition 

ventral area dorsal stream damage

• sensory perceptual spatial neglect: right posterior parietal cortex → can’t draw things on the left = left visual field → right cortex

• recovery: more detail revealed over time but in the beginning prefer the right side

• can also result in language deficits - ignore the first part of the word when writing ONLY

• spatial neglect of recalled memories: same posterior parietal circuits are responsible for perception and memory

dorsal area dorsal stream damage

• personal neglect: body parts contralateral to the lesion

• difficulty reaching for objects or orienting hand properly to grasp

• no problem in the dark - not a motor deficit but a perceptual one

posterior parietal neurons (DD)

• increase in firing for glancing at object

• rlly high firing for touching object

• important for interacting with objects

primary sensory cortex

• inputs: sensory regions of the thalamus

• RFs: small and unimodal

• anatomical layout of RFs: orderly maps that relate to receptor organization

• damage: simple sensory loss

• connectivity: adjacent regions (V1 connect to V2) and same modality

association cortex

inputs: sensory and association regions of the cortex

RFs: large and multimodal - jennifer aniston neuron (visual + smell)

Anatomical layout of RFs: varies, purpose of anatomical organization is poorly understood

Damage: disordered perception/cognition and sensory detection

connectivity: nearby sensory regions but also association cortices near and far

hippocampus

• where the 2 streams converge

• peak of associational/convergence hierarchy (highest order representation)

pathway

• ventral stream → LEC → hippocampus

• dorsal stream → MEC → hippocampus