Topic 7: Object Recognition

Ventral Visual System

A processing stream that includes areas ventrally situated toward anterior temporal regions and devoted to processing stimuli and extracting meaning

Agnosia

Inability to process sensory information; can refer specifically to visual agnosia which is the inability to recognize objects.

Visual Agnosia

Inability to recognize objects in the visual modality that cannot be explained by other causes.

Apperceptive Agnosia

Can’t form a perception or a meaningful whole, due to a lesion in the occipital regions

Associative Agnosia

The ability to perceive objects but unable to assign meaning or recognize their use or associated knowledge. Lesion to bilateral occipitotmeporal

Prosopagnosia

A type of associative agnosia specifically for faces, where the individual cannot recognize familiar faces. Lesions on the right hemisphere usually. Developmental means it was worsening from birth or early childhood due to abnormal brain development or connectivity.

Receptive Fields

Areas in the visual system where a stimulus will influence the firing of a neuron; become larger as one moves along the ventral stream.

Category-Specific Agnosia

A form of agnosia where patients struggle more with identifying living things compared to inanimate objects.

FFA (Fusiform Face Area)

A region in the human brain that specializes in face recognition, part of the ventral visual stream.

Implicit Processing

The unconscious recognition of familiar faces, allowing for emotional responses without explicit identification.

Ventral Stream

A system in the brain responsible for processing object recognition, particularly the identification of objects based on their visual properties.

Viewpoint Dependent Recognition

The theory that object recognition depends on multiple representations of the same object, specific to different viewpoints.

Viewpoint Independent Recognition

A theory suggesting that the brain constructs a 3D representation of objects based on their structural components, independent of viewpoint.

Lateral Occipital Complex (LOC)

A region in the brain responsible for recognizing objects at a perceptual structural level, supporting recognition across variations in size and form. Cue invariant, shape driven, no semantic information

Repetition Suppression Effect

A decrease in the BOLD signal in fMRI studies when a stimulus is repeated, indicating neural adaptation.

Sparse Coding

A coding theory where a small, specific group of neurons responds to a particular object. (Eg. grandmother cell) ONE neuron to one stimiulius

Population Coding

A coding theory where a pattern of activity across a large number of neurons represents an individual object.

Auditory Agnosia

The inability to link auditory information to its meaning despite normal basic auditory processing.

Agnosia

A condition characterized by the inability to recognize objects despite having intact sensory perception.

Facial Recognition Areas

Specialized brain regions such as the Occipital Face Area (OFA) which processes individual parts and Fusiform Face Area (FFA) that process facial features and configurations (right)

Pros of larger receptive fields

Allows whole objects to be detected, identified regardless of size/location, include central vision and increases sensitivity to stimuli.

Herpes encephalitis

causes brain swelling, worsened agnosia for living things NOT objects

kinesthetic codes

know how to interact with inanimate objects based on the affordability

perceptual invariance

the ability to recognize objects as the same despite changes in viewpoint, lighting, and size.

HMAX model

invariance is built by combining units tuned to different featuresto create a hierarchy of visual processing.

Viewpoint dependent

recognition refers to the process of identifying objects based on the specific angle or position from which they are viewed, leading to varying representations for different viewpoints.

Viewpoint independent

perceptual system extracts structural information to build a 3D representation

Right ventral stream

mostly processes whole forms and object recognition, linking visual perception to object representations.

Left ventral stream

recognizes parts of objects

Configurational processing

is a perceptual approach that focuses on how objects are recognized based on their arrangement and configuration rather than just their individual parts. (face with features flipped)

Superior temporal sulcus (STS)

dynamic features (lip reading, expressions, etc.) and biological motion

Why are faces special?

processed holistically NOT by parts (whos nose? vs whos front door?)

Parahippocampal place area (PPA)

specialized area in the brain for recognizing scenes and places, contributing to the understanding of spatial layouts.

Extrastriate body area (ERA)

prefer human body/parts compared to other objects or organisms

Visual word form area (VWFA)

visual representation of words (left lobe)

Verbal auditory agnosia

pure word deafness where there is a deficity in mapping (can write and produce tho)

Nonverbal auditory agnosia

understand the information but can’t map nonverbal sounds (bark doesnt = dog)

somatosensory agnosia/tactile asymbolia

can’t recognize something by touch stimuli, despite having intact sense of touch.