Object Perception Flashcards
Visual Processing: Primary Visual Cortex V1: receives info... Extrastriate cortex: - Topographical organisation – - Presents stimuli in VF, mapping... - contralateral and... - disproportionate..
- damage =
- partial damage =
the retino collicular pathway:
about visual input
rest of occipital lobes
maps the outside visual world in a map-like way
the regions sensitive to stimuli, reproduces the external map
inverted
(more cortex devoted to centre of visual field)
cortical blindness
blindness to part of visual field
optic nerve > midbrain (superior colliculus) by-passes V1
Visual Processing: Extrastriate Cortex
Regions that analyse…
The Dorsal and Ventral Processing Streams:
Dorsal Stream:
Ventral Stream:
more specific features
e.g., edges, contours, shapes, colour, angle, movement
(“where”) - location and position/movement
(“what”) - item identification and colour/form
Ventral Stream – Extrastriate Cortex ventral regions specialise in... - basic form perception - colour analysis contralaterally organised (deficits only after bilateral damage)
detailed analysis of visual stimuli
identifying edges, contours and shapes (lateral parts)
(medial parts)
VEC – Form Analysis (lateral):
Damage:
Mr. S: able to detect… and unable to….
Intact Objects minus Scrambled Objects > lateral…
person can “see” but may be functionally blind
small differences in luminance, wavelength and area, and movement
distinguish between two objects
occipital area activation
VEC – Colour Analysis (medial):
fMRI study:
video contains different various images (static and moving)
medial portion of ventral extrastriate cortex
include area hV4
regions more activated for…
This region activated when colour is…
fMRI study: (1) view coloured vs. B&W wheels, (2) recall colours of familiar items vs. recall function
Damage =
colour images than for B&W images
imagined rather than seen
Achromatopsia (cortical colour blindness)
no conscious awareness of colour
Higher-Level Perception (Ventral Stream): Impairments Kevin Chappell: – can see but cannot... – can describe... – can infer from... – form analysis is... – can identify and draw... – can’t identify more... – unable to draw from... – can recognise...
HJA:
– identifies objects…
recognise objects (living in a world of unidentifiable objects)
objects
colour/ form and shape of objects without recognition
persevered
simple shapes and basic outlines of figures
complex shapes - difficulty integrating complex objects to understand it and recognise it
memory (loss of visual knowledge)
faces
in a piecemeal way
Higher-Level Perception: Impairments It is still a... 1. visual quality matters: 2. knowledge of item, when tested... 3. participants confuse...
perceptual problem (not a loss of knowledge about objects)
participants better at identifying items when all features are clearly visible
verbally may be entirely normal
visually similar items
What is Higher-Level Object Perception?
- recognition of….
- visual world is…
- need to store ‘templates’ that…
- this information is stored in ventral portions of…
meaningful, complex stimuli needs to be rapid and automatic.
degraded and incomplete, need to be able to recognise an item quickly
represent meaningful visual configurations, which can be accessed readily even with incomplete visual information
occipital and temporal lobes, anterior to more basic form perception regions
Specialisation According to Category: Faces Double Dissociation Lincoln Holmes: – selective inability to... – able to identify... – knowledge is intact...
recognise faces
inanimate objects rapidly
face recognition is not
Higher-Level Object Perception: Neuroanatomy
different regions specialise in…
fMRI: regions that respond more strongly to their ‘preferred’ type of stimulus
different classes of items
RH (faces) – LH (words).
Specialisation According to Category: Words
- key region involved:
- LH is specialised for…
Damage to VWFA region = o problems reading but not... o can read... o reading slow, time increases... o letter-by-letter... o letters no longer...
the visual word form area
recognising words
pure alexia writing single letters OK as words gets longer reading strategy present in parallel
Summary of Ventral Stream Processing Function (1) Construction of a... (2) Basic analysis of... (3) Analysis of...
Region
(1) ?
(2) ?
(3) ?
Properties
(1) respects spatial organisation of VF and…
(2) analysis of different features in different regions and…
(3) different regions dedicated to different categories of items and…
- V1 constructs a map respectful of. physical reality of VF, distorts in various ways to allow other processes to process different information, regions of brain generates map-like representations of VF
- Not map-like, more specialisation in different regions for different physical features.
- Areas specialised for meaning and category, anterior to other areas, engaging temporal lobes, one hemisphere better at it than other
topographic map of the visual fields
form, edges, contours, shapes and colours
complex stimuli, extraction of meaning
Primary Visual Cortex
Specific regions of extrastriate cortex
Specific ventral regions at temporal-occipital border
contralateral, inverted, disproportionate
contralaterally organised
hemispheric specialisation
Principles Visual processing is a... As you go up, knowledge... Organisation becomes..... Less...
hierarchy
counts more, physical aspects count less
less contralateral/topographical, more asymmetric
bottom up, more top down
