Lecture 6 - Object Recognition Lecture Notes

These flashcards cover primary concepts of object recognition, including the dorsal and ventral pathways, types of visual agnosia, specific brain regions like the FFA and LOC, and theoretical models of stimulus recognition.

Visual agnosia

The inability to recognize stimuli even when sensory input is intact, as seen in Patient G.S. who could identify low-level properties like color and lines but could not recognize objects.

Dorsal Stream

A visual pathway specialized for spatial perception that determines where an object is in space.

Ventral Stream

A visual pathway specialized for object perception and recognition that determines what an object is.

Dual Pathway Distribution

$60\%$ of the neurons in the dorsal stream exclude the fovea to focus on the peripheral field, whereas the ventral stream centers its focus on the fovea to identify objects.

Anomia

A condition involving trouble naming objects; distinct from visual agnosia because patient D.F. could name objects when they were held in her hand but not by sight alone.

Lateral occipital cortex (LOC)

A region in the ventral stream activated by both familiar and new shapes; its activity is found to be cue invariant, meaning it does not care about specific features.

Gnostic Units

Individual cells that signal the presence of a known stimulus, forming the basis of the grandmother hypothesis.

Grandmother hypothesis

A bottom-up approach to object recognition suggesting that specific neurons are dedicated to recognizing specific stimuli.

Ensemble coding hypothesis

A theory suggesting that stimulus recognition results from the collective activation of many neurons rather than a single gnostic unit.

Encoding

The process of how sensory stimulus features are represented in neural activity.

Decoding

Predicting the stimulus an individual has seen by classifying, identifying, and reconstructing it through brain imaging and neuronal activity.

Multi-stable Perception

A phenomenon where perception alternates after observing an illusion or binocular rivalry for a specific period of time.

Fusiform Face Area (FFA)

A region along the ventral surface of the temporal lobe selective to faces that helps determine the "what" of a face.

Face Perception Aspects

Identified by Chang & Tsao ($2017$) as shape (processed in the lateral portions of the inferior temporal cortex) and appearance (processed in the anterior portions).

Parahippocompal face area

A selective visual region identified by Epstein & Kanwisher ($1988$) as being selective for landscape scenes.

Triple Dissociation

A finding by Pitcher et al. ($2009$) using TMS where targeting the OFA impaired face discrimination, rLO impaired object discrimination, and EBA impaired body discrimination.

Apperceptive visual agnosia

The inability to form a coherent percept, resulting in difficulty with object constancy and recognizing objects in atypical presentations.

Integrative visual agnosia

A failure where a patient can perceive parts of an object but is unable to integrate them into a coherent whole.

Associative visual agnosia

A state of perception without recognition where a patient can see objects but cannot identify them or describe their functions.

Prosopagnosia

The inability to recognize faces, often caused by impaired connectivity between the Fusiform Face Area and other face processing regions.