5. The Visual Cortex/Beyond Scenes and Objects

January 20, 2026

The organization of ____ represents an ‘electronic map’ of the retina which is ____.

V1; Retinotopic

Retinotopic

Two points that are close together on an object are also represented in parts of the cortex that are close together.

Cortical Magnification

A small area of the fovea is represented by a large area on the visual cortex.

• Contributes to high acuity vision

Cortical Magnification

Describes the disproportionate amount of visual cortex dedicated to processing stimuli from the center of your vision (fovea) compared to the periphery.

Single-cell Recordings

A technique using microelectrodes to measure the electrical activity (voltage or current changes) of an individual neuron or small group of neurons.

The red region (fovea) takes up ____ of the visual field than the blue region (in the _____), yet activates a _____ chunk of the visual cortex.

The red region (fovea) takes up less of the visual field than the blue region (in the periphery), yet activates a larger chunk of the visual cortex.

Visual Field vs Representation in V1

IT Neurons

Neurons in the inferotemporal (IT) cortex respond to more complex stimuli than neurons in V1.

The _______ has _______ which tend to respond best to faces.

The Fusiform Face Area (FFA) has neurons which tend to respond best to faces.

Sensory Coding

Refers to the way perceived objects are represented through neural firing.

How might sensory coding of more complex objects be accomplished? Three (general) theories are…

• Specificity Coding

• Population Coding

• Sparse Coding

Specificity Coding

Specific (individual) neurons respond to specific stimuli.

Leads to the grandmother cell hypothesis.

Grandmother Cell Hypothesis

A hypothetical neuron that uniquely fires for one specific, complex concept, like seeing your grandmother, acting as a highly specialized "recognizer" for that single item.

Quiroga et al. (2005, 2008)

Measure the response of individual neurons in humans undergoing surgery for epilepsy, finding neurons that seemed to respond to the presentation of specific faces.

Reported results for a patient undergoing surgery for epilepsy had the activity of individual neurons in their temporal lobe recorded.

Neurons were found that responded to images of one specific actor but not others, which could potentially represent an example of specificity coding.

Problems with specificity coding…

• Too many different stimuli to assign specific neurons

• Most neurons respond to a number of different stimuli

• If you only observe a single neuron firing in response to a single stimulus, how do you know if other neurons (which aren’t currently being measured) are also firing?

Population Coding

Pattern of firing across many neurons codes specific objects.

• Large number of stimuli can be coded by a few neurons

• In theory, could code for a very large number of representations

Sparse Coding

Only a relatively small number of neurons are necessary to code for each concept/identify, etc.

• This theory can be viewed as a midpoint between specificity and population coding

• Some evidence across modalities for sparse coding, at least for some things

_____ _____ _____ structures are extremely important for memory.

Signals coming from IT cortex project to _____.

Medial temporal lobe (MTL) structures are extremely important for memory.

Signals coming from IT cortex project to MTL.

Modularity

Proposes the mind isn't a single general processor but a collection of specialized, independent modules for different tasks, each with distinct functions, operating characteristics, and sometimes location.

Modularity and the FFA

The way we process faces is somehow ‘special’ and may involve some dedicated neural mechanisms, or modules, that are specialized for processing particular kinds of stimuli.

Evidence: The fact that temporal lobe damage in humans can result in prosopagnosia (an inability to perceive faces).

Inversion Effects

Inversion effects are strong for faces, and are said to occur for stimuli that people have difficulty noticing unusual details (anomalies) in when turned upside down.

Experience-Dependent Plasticity

The brain's lifelong ability to reorganize its neural connections (synapses) in response to unique life experiences, learning, and environmental stimulation.

Expertise Hypothesis

Proposes that brain regions (e.g. FFA), thought to be face-specific, actually process any object category for which a person gains extensive, fine-grained visual expertise.

____ ____ ____ responds best to spatial layout.

Parahippocampal place area responds best to spatial layout.

____ ____ ____ responds best to pictures of full bodies and body parts.

Extrastriate body area (EBA) responds best to pictures of full bodies and body parts

Distributed Representation

A cognitive and neural concept where a concept isn't stored in one specific spot but as a pattern of activation across many neurons or processing units, with each unit contributing to multiple concepts, mimicking how the brain efficiently encodes complex info.

True or False: Distributed Representation and Localization of Function can be compatible/complimentary.

True.

Ishai et al. (2000)

Used fMRI to image neural activation in humans resultant of presenting stimuli from three categories: houses, faces, and chair.

Image ‘a’ demonstrates differences in the location of maximal activation associated with each stimulus category.

• This is consistent with the idea of localization of function.

Image ‘b’ demonstrates that each of these stimuli category activate widespread areas of cortex.

• This supports the idea of distributed representation.

Huth et al. (2012)

Showed participants various stimuli coded as belonging to various categories, then examined neural activation as a function of those categories.

Noticed multiple points across the cortex are coded as belonging to the same category of stimuli (e.g. humans).

• Suggests that some kinds of stimuli are processed in more than one location

• This may also depend in part on what you’re doing with a given stimulus

Multidimensional Stimuli

Sensory inputs or data defined by multiple, interacting features (dimensions) rather than a single one, requiring complex perception and processing.

E.g. Facial Stimuli

• Emotional aspects

• Where someone is looking

• How parts of the face move

• How attractive a face is

• Whether the face is familiar

Function of the Occipital Cortex

Occipital Cortex (OC): Initial processing.

Function of the FFA

Fusiform Face Area (FFA): Basic face processing.

Function of the Amygdala

Amygdala (A):

• Emotional reactions: face expressions and observer’s emotional reactions).

• Familiarity: familiar faces cause more activation in the amygdala and other areas associated with emotions.

Function of the Frontal Lobe

Frontal Lobe (FL): Evaluation of attractiveness.

Function of the Superior Temporal Sulcus

Superior Temporal Sulcus (STS):

• Gaze direction

• Mouth movements

• General face movements

Inverse Projection Problem

Refers to the task of determining the object responsible for a particular image on the retina.

This is not straightforward, as any given two-dimensional image formed on the retina could be formed by many different three-dimensional objects in the environment.

Occlusions

A process whereby something is hidden or obscured from prominence or view. Objects can appear blurred, fuzzy, or distorted in various ways.

Viewpoint Invariance

The ability to recognize an object despite changes in the observer's viewing angle

Perceptual Organization

Refers to the process by which elements in our environment get grouped together to create our perception of the environment. This involves both:

• Grouping (‘putting together’ objects)

• Segregating (separating objects)