17 - Visual Processing of Objects Flashcards
How many visual areas are there and how are they arranged?
30+ visual areas
Arranged along two major pathways; dorsal and ventral streams
Describe the dorsal and ventral streams
Dorsal
- primary visual cortex to posterior parietal lobe
- “where” and “how” (spatial location, vision to guide action).
Ventral
- primary visual cortex to inferior temporal cortex
- “what” (shape and object identity and conscious perception)
What is the difference with the what/where theory and perception vs action theory of the visual streams?
What/Where: functional characterisation in terms of information content.
Perception vs Action: functional characterisation in terms of process
Both are correct and co-exist
Explain the hierarchical organisation of the ventral stream that was determined by studies on macaques
Early visual areas (V1, V2)
- neurons respond to simple edges and points of light (textures and scrambled objects in humans)
- small receptive fields
- retinotypically organised
Intermediate areas (V4, TEO)
- neurons respond to moderately complex features
- larger receptive fields
- restricted to one visual quadrant
High level areas (IT)
- neurons respond to complex objects (faces, hands)
- very large receptive fields
- NO retinotopic organisation
What area of the brain is more activated by full objects
Lateral occipital complex - LOC
More anterior area
How does the transition of perceiving part-based to full objects graduate in the brain?
From posterior to anterior
What are the two divisions of the LOC
LOC = human “object area”
Lateral surface of occipital lobe (LO)
Ventral surface of occipital and temporal lobes (vOT)
Describe binocular rivalry displays
Visual input remains the same but percept flips from one to another.
Create conflict from the rival stimulus, and relieve this by our perception changing between the two inputs.
What do human fMRI studies using binocular rivalry reveal?
V1, V2, V4 and LOC NOT differentially activated by identified vs unidentified stimuli.
vOT activity correlates with recognition not just presence of stimulus.
vOT correlation with recognition stronger in more anterior parts
Where is the FFA located and what does it specialise in?
Fusiform gyrus
Faces
Where is the PPA located and what does it specialise in?
Parahippocampal place area
Parrahippocampal gyrus
Buildings and place scenes
Where is the EBA located and what does it specialise in?
Extrastriate body area located in right occipito-temporal cortex
Body parts
How if functional specialisation inferred?
Selectivity of the information processed
Spatial clustering
Damage to that area disrupts processing of a specific class of objects
Describe the Domain-Specificity Hypothesis by Kanwisher
Anatomical modules in the brain are specialised for different categories (FFA, PPA, EBA, VWFA)
Organisational principles are information content and the modules are innate
What did Gauthier and Tarr believe abuot the processing requirements of the ventral stream?
Organisational principle is process and modules are shaped by experience.
E.g. FFA related to expertise in discriminating members of perceptually homogenous class (birds, greebles)
PPA not place, but spatial layout
