PSYC3014 quiz 2

two visual streams

dorsal stream

• from primary visual cortex → posterior parietal lobe

• computes spatial location + guides action using vision

• strong interactions with motor system

ventral stream

• from primary visual cortex → inferior temporal cortex

• computes shape + object identity

• contributes to perception + awareness

1. prefrontal cortex (spatial working memory) “where”

2. premotor cortex (action) “how”

3. medial temporal lobe (navigation) “where” on environmental scale

hierarchical organisation of ventral stream

• early visual areas (V1, V2): neurons respond to simple edges + points of light, small receptive fields

• intermediate areas (V4): neurons respond to moderately complex features, larger receptive fields

• high level areas (IT): neurons respond to complex objects (face, hands), very large receptive fields

lateral occipital complex

• human “object” area

• two divisions: LO (lateral surface of occipital lobe) and vOT (ventral surface of occipital + temporal lobe)

• spatial bias: LOC activity is invariant across location BUT objects are processed more efficiently in their usual spatial location

object representation in LOC

• high level object shape representation

LO (lateral division)

• more sensitive to changes in location + size, 2D shape features

• LOtv is activated by visual + tactile input, soundscapes + auditory shapes

vOT (ventral division)

• more invariant to changes in location + size, sensitive to 3D shapes, not activated by tactile input

• codes abstract identity of representation

• vOICe: visual imagery is converted to soundscape for blind people

  • after training, LOtv responds to vOICe objects

regional organisation of ventral stream

faces processing network

• FFA (fusiform face area): ventral temporal cortex

• OFA (occipital face area): early face processing

• STS (superior temporal sulcus): social/emotional aspects of face

• ATA (anterior temporal area): encoding identity

places processing network

• PPA (parahippocampal place area): encoding large objects (scenes/houses)

• retrosplenial cortex + posterior parietal lobe: spatial navigation + orientation

• hippocampus: spatial layout

word processing network

• VWFA (visual word form area): words/letters

fMRI adaptation

• BOLD response decreases with repetition

• if adaptation persists when a stimulus changes along a dimension, the same neural population responds; if adaptation recovers, a different population is engaged

object processing disorders

visual agnosia: failure to make sense of visual information, but they are NOT blind

• apperceptive: recognition deficits linked to perceptual processing problems

  • visual form agnosia: very severe, cannot discriminate shapes, copy drawings or read

• associative: normal percepts but failure to link to stored memory/knowledge

  • visual object agnosia: inability to recognise objects

  • prospoagnosia: inability to recognise faces

  • lesions in temporal + occipital regions (vOT)