Where and What Pathways

• Feature detection and object recognition are key aspects of perception
• Understanding how brains identify visual features is important

Where and What Pathways

• Ungerleider and Mishkin's research in 1982 explored "where" and "what" pathways in the brain
• Ablation, the destruction or removal of nervous system tissue, was used as the research method
• Monkeys were tested behaviorally to assess their capacity after ablations
• Object discrimination tasks involved the monkey picking the correct shape
• Landmark discrimination involved picking food closer to a cube
• Either the temporal or parietal lobe was ablated, leaving the rest of the brain intact
• This was achieved surgically or by chemical injection
• Performance was retested post-ablation

Dorsal vs. Ventral Pathways

• Ablating the parietal lobe (dorsal pathway/where) caused difficulty solving landmark problems and determining object location
• Ablating the temporal lobe (ventral pathway/what) caused difficulty in object discrimination regarding object identity
• The occipital lobe is the common source area (primary visual receiving area) for both pathways

What and How Pathways

• Milner and Goodale proposed "what" and "how" instead of "what" and "where" in 1995
• Taking action involves knowing object location (where pathway) and physically interacting with it
• The ventral stream is for perceiving objects (what pathway)
• The dorsal stream is for taking action, such as picking up an object (how pathway)
• Neurons in the parietal cortex respond both when a monkey looks at an object and reaches for it
• Reaching for a wool ball involves information about the ball's location and hand movement

Neuropsychological Evidence

• Damage to the ventral lobe in humans impacts behavior
• Patient D.F., a 34-year-old female, suffered damage to her ventral pathway from carbon monoxide poisoning
• As a result, she was unable to match the orientation of a card, but could still "mail" it through a slot
• This suggests that judging orientation and coordinating vision for action are separate mechanisms

Dual Stream Theory

• Low spatial frequency tuning is associated with the magnocellular layers
• High temporal frequency is associated with the magnocellular layers
• There is temporal info processing in the magnocellular layers
• High spatial frequency tuning is associated with the parvocellular layers
• Low temporal frequencies is associated with the parvocellular layers
• Hue discrimination is associated with parvocellular layers

Brain Specialization

• Different brain areas handle different functions like language and hearing
• "Modularity" is how different brain areas handle various algorithmic functions
• In area V1 and beyond are feature detectors
• Building Receptive fields build complexity occurs via spatial pooling of inputs
• Positional invariance is indicated by the multiple crosses

Visual Hierarchy

• The visual system has multiple spatial scales
• Neurons in the visual system are evolved to get contour information
• Morph images and scaling also help with processing
• "'Low' spatial frequency filters encode coarse luminance variations in the world overall shape"
• "'High' spatial frequency filters respond to the fine spatial structure of the world for detail

Functional Areas

• Visual area is responsible for sight, image recognition, and image perception
• The association area is for short-term memory, equilibrium and emotion
• The motor function area initiates voluntary muscles
• Broca's area controls muscles of speech
• The auditory area receives sound
• The emotional area is where processes like pain and hunger occur

Marr's Model of Vision

• Photoreceptors encode light intensity
• Retinal ganglion cells encode local contrast
• Primary visual cortex encodes oriented lines
• Area MT+ and parietal cortex are responsible for grouping and segmenting surfaces
• The infero-temporal cortex constructs the 3D model, responsible for complex object recognition

Face Selectivity

• Highly complex selectivity of receptive fields shown through face-sensitive neurons
• The fusiform face area is located in the inferior temporal cortex

Problems of Object Recognition

• Vision is an inverse problem
• Perception is impacted by scale and different vantage points
• Objects can be hidden or blurred
• The ability to recognize an object from different viewpoints is viewpoint invariance

What is Object Recognition?

• It is a match between visual input (processed through the ventral stream) and mental representation
• The perirhinal cortex is involved in visual recognition memory (prototypes of objects)
• Abstraction involves filtering spatial frequency

Theories of Object Recognition

• Template Matching: there would be a template stored in the long-term memory for each letter or numeral
• Structural descriptions: A structural description consists of a set of propositions which are symbolic but not linguistic about a particular configuration.
• Recognition by components (by Biederman): Complex objects are described as spatial arrangements of basic component parts.

The shape primitives are called geons.

• Neurons of the interotemporal cortex show sensitivity to geon rather than metric variation
• Models of the brain indicate a modular view of object recognition

Theories

• "Nonaccidental" properties of bricks and cylindres include line intersections
• "Jennifer Aniston" cells were discovered while monitoring the brain of a patient during an epilepsy surgery
• Undergoing surgery for epilepsy, the output of cells in IT (infero-temporal cortex) was monitored
• During surgery the patient was being shown images of various faces.
• One cell responded only to pictures of Jennifer Aniston"

Models

• Configurational models are being recognized
• The spatial relations are among those parts
• There is a common structure of the the extent to which those spatial relations deviate from the prototype, or "average," object.
• Prosopagnosia occurs when the FFA is damaged
• A painting example of this is "Nude Descending a Staircase" by Marcel Duchamp, 1912