3 perception and cognition Flashcards
What is the function of the Lateral Geniculate Nuclei ?
in thalamus
integral for early steps in colour processing, where opponent channels are created that compare signals between the different photoreceptor cell types
What is the retina-geniculate striate pathway?
connects LGN to V1, serves to relay visual information from retina to cortex
What is the MST: Medial Superior Temporal Cortex for?
Involved in optic flow, identification of pattern of motion in the parietal lobes
What is the Inferotemporal cortex IT for?
Its the final stage of the ventral pathway in the temporal lobes
What exactly is part of the ventral stream?
WHAT
recognition/identification
high spatial frequencies - details
long-term stored representations
slow speed
high consciousness
allocentric, object-centered frame of reference
mainly foveal or parafoveal visual input
small effects of monocular vision
What exactly is part of the dorsal stream?
HOW
visually guided behaviour
high temporal frequencies - motion
short-term storage
fast speed
low consciousness
egocentric, viewer-centred frame of reference
across retina visual input
large monocular vision effects, eg motion parallax
Which brain areas are involved in the ventral stream?
V1 -> V2 -> V3 (in form processing) -> V4 (colour processing) -> IT (info
temporal cortex - final stage - object recognition)
Primary Visual Cortex (V1): Occipital lobe.
Function: Initial processing of visual information, such as orientation, edges, and motion.
V2 (Secondary Visual Cortex): Occipital lobe, adjacent to V1.
Function: Further processing of visual information, integrating features like color and complex shapes.
V4:Occipital and temporal lobes.
Function: Specialized in color processing and the perception of form and shape.
Inferotemporal Cortex (IT Cortex): Temporal lobe.
Function: Involved in high-level visual processing, particularly in object recognition and identification, such as recognizing faces and complex shapes.
Fusiform Gyrus: Temporal lobe, within the IT cortex.
Function: Specialized in facial recognition (fusiform face area) and processing of detailed visual features.
Which brain areas are involved in the dorsal stream?
V1 -> V2 -> V3 -> V5 (motion processing, MT) -> MST (computation such as
optic flow)
Middle Temporal Area (MT or V5): Temporal lobe (posterior part).
Function: Highly specialized in detecting motion, speed, and direction of moving objects.
Posterior Parietal Cortex: Parietal lobe.
Function: Integrates spatial information and guides movements based on the location and motion of objects. It plays a crucial role in hand-eye coordination and spatial awareness.
Superior Parietal Lobule: Parietal lobe.
Function: Involved in spatial orientation, reaching, and grasping movements, as well as in the integration of sensory and motor information for action planning.
What are some criticisms for the two-pathway hypothesis?
First, there are complex interconnections among visual cortical areas.
Second, the brain areas within the ventral pathway are more than twice as large as those within the dorsal pathway.
Third, cells in the lateral geniculate nucleus respond fastest when a visual stimulus is presented followed by activation of cells in VI
What does the functional specialisation theory posit according to Zeki (1993, 2001)?
object attributes can occur in unpredictable combination
Vl and V2 They are involved at an early stage of visual processing.
They contain different groups of cells responsive to colour and form.
V3 and V3A Cells in these areas respond to form (especially the shapes of
objects in motion) but not colour.
V4 The majority of cells in this area respond to colour; many are also
responsive to line orientation.
V5 This area is specialised for visual motion. In studies with macaque monkeys, Zeki found all the cells in this area responded to motion but not colour. In humans, the areas specialised for visual motion are referred to as
MT and MST.
How does form processing work?
V1-4
neurons in inferotemporal cortex respond to specific semantic categories
Recognizing shapes, edges, and contours of objects.
Primarily involves the ventral stream.
Primary Visual Cortex (V1): Initial detection of edges and orientations.
V2: Combines simple features from V1 to form more complex shapes.
V4: Further processes shapes, focusing on complex forms and object recognition.
Inferotemporal Cortex (IT Cortex): High-level processing where specific objects (e.g., faces, tools) are recognized based on form.
Visual information about edges and contours is first detected by V1.
This information is then integrated in V2 and V4 to identify and differentiate between various shapes and patterns.
The IT cortex links these shapes with memory to identify the object.
How does color processing work?
Perception and differentiation of colors.
Also primarily involves the ventral stream.
Primary Visual Cortex (V1): Detects color information through color-sensitive neurons.
V2: Processes basic color contrasts.
V4: Specializes in color perception, enabling the discrimination of different colors and integrating color with form.
Cones in the retina detect different wavelengths of light corresponding to colors.
Color information is processed in V1 and passed to V2 for further refinement.
V4 integrates the color information, helping in recognizing objects based on their color, and maintaining color constancy under varying lighting conditions.
How does motion processing work?
V5
less important for processing low-speed motion
60% of cells in V5/MT respond to binocular disparity
50% to stimulus orientation
90% to direction of motion
Detection of movement, speed, and direction of objects.
Primarily involves the dorsal stream.
Primary Visual Cortex (V1): Initial detection of motion begins with the processing of temporal changes in visual information.
Middle Temporal Area (MT or V5): Specializes in detecting the direction and speed of moving objects.
Posterior Parietal Cortex: Integrates motion information with spatial positioning, helping to guide movements in response to moving objects.
Motion is first detected by V1, where neurons are responsive to changes in light and contrast over time.
MT/V5 processes this information to determine the direction and velocity of the motion.
The posterior parietal cortex uses this information to guide actions, like reaching for a moving object or navigating through space.
What are the disorders called when you have deficits in form/motion/colour processing?
achromatopsia - colour perception
visual form agnosia (very rare) - form perception
akinetopsia - motion perception
What is the binding problem?
the issue of integrating different types of information to produce
coherent visual perception
feedforward processing + recurrent processing
binding by attention?
-> illusory conjunctions related to attention mechanisms
binding by temporal synchrony?
mechanical
neurons tend to synchronize (discharge synchronously)
