Perception: The Act of Perceiving - Neural Foundations and the Visual System

Vocabulary practice flashcards covering neuroanatomy, signal transmission, cortical pathways, ocular structures, and photoreceptor physiology from Lecture 2 of Perception.

Central Nervous System (CNS)

The primary control center of the nervous system responsible for transmitting and processing information across sensory, association, and motor levels.

Sensory Level (CNS)

The information-handling level of the central nervous system composed of energy detectors and receptors that receive environmental input.

Association Level (CNS)

The information-handling level of the central nervous system that functions as a processing system to interpret and give meaning to sensory input.

Motor Level (CNS)

The information-handling level of the central nervous system that directs and executes physical actions through the motor system.

Neurons

Specialized communication cells (numbering approximately $86\text{ billion}$ in the nervous system) that share structural features and transmit electrical and chemical signals.

Neuroglia

Non-neuronal supporting cells in the nervous system that maintain structural integrity, provide support, and protect neurons.

Synapse

The junction where an impulse triggers synaptic vesicles to release neurotransmitter molecules into the synaptic cleft, which then bind to specific receptor sites on a receiving neuron.

Action Potential

A rapid electrical impulse generated along an axon when depolarization reaches a threshold of approximately $-50\,\text{mV}$, reversing the resting charge of $-70\,\text{mV}$ up to roughly $+30\,\text{mV}$ or $+40\,\text{mV}$.

Depolarization (Excitatory)

A decrease in electrical potential across a neuron's membrane making the internal charge less negative, moving it toward the threshold needed to trigger an action potential.

Hyperpolarization (Inhibitory)

An increase in electrical potential across a neuron's membrane that makes the internal charge more negative than $-70\,\text{mV}$, decreasing the likelihood of firing an action potential.

Refractory Period

The recovery interval following an action potential during which a neuron cannot fire or requires a stronger than normal depolarizing stimulus to fire.

Receptive Field

The specific region of sensory receptors that, when stimulated, alters the electrical activity and firing response of a target neuron.

Primary Visual Cortex (V1)

The initial visual processing region in the occipital lobe responsible for basic visual features, preliminary delineation, and receiving input from the optic nerve pathway.

Area MT/V5

A cortical area located in the visual pathway specialized specifically for motion detection.

Dorsal Stream

A visual cortical processing pathway directed superiorly that is responsible for determining the spatial position and location of visual stimuli.

Ventral Stream

A visual cortical processing pathway directed inferiorly into the temporal regions that determines the identity and meaning of visual stimuli.

Bottom-Up Processing

A perceptual process built upward from raw physical stimuli reaching sensory receptors, starting with simple features and ending with a complex mental representation.

Top-Down Processing

A perceptual process driven by stored knowledge, experience, context, and expectations that actively supplements and fills in incoming sensory data.

Modularity

The operational principle that distinct, relatively independent yet interconnected brain structures (modules) are specialized to process specific classes of stimuli.

Parahippocampal Place Area (PPA)

A specialized cortical module that shows preferential neural activation in response to scenes and spatial layouts.

Extrastriate Body Area (EBA)

A specialized cortical module that responds selectively to visual representations of human bodies and body parts.

Distributed Representation

The concept that the perception of a stimulus is mediated by neural activity distributed across a wide network of multiple brain regions, rather than confined to a single area.

Lesioning (Ablation)

An experimental technique in animal research where a specific brain region is surgically removed or destroyed to assess which perceptual capacities remain.

Perceptual Psychophysics

The quantitative study of the relationship between physical stimulus characteristics and psychological sensory experience, typically identifying detection thresholds where a stimulus is detected $50\%$ of the time.

Accommodation

The process by which the ciliary muscles alter lens thickness to increase refractive power, bringing the focus point forward onto the retina when viewing nearby objects.

Retina

The light-sensitive layered neural tissue lining the back of the eye that converts chemical and electrical events into neural signals sent to the visual cortex via the optic nerve.

Fovea

A small region of central focus on the retina subtending approximately $1^\circ\text{–}2^\circ$ of visual angle, exclusively populated by a high concentration of cones and lacking rods.

Blind Spot (Optic Disc)

The retinal site where ganglion cell axons bundle to form the optic nerve and exit the eye, entirely devoid of photoreceptors.

Rods

Photoreceptors (approximately $120\text{ million}$ per eye) containing rhodopsin that provide high-sensitivity monochromatic vision in dim light, but are completely absent from the fovea.

Cones

Photoreceptors (approximately $6\text{ million}$ per eye) containing odopsin that mediate daylight and color vision across three subtypes: Red ($60\%$), Green ($30\%$), and Blue ($5\text{–}10\%$).

Visual Pigment

Light-sensitive molecules situated in photoreceptor outer segment disks consisting of a protein component (opsin) bound to a light-absorbing molecule (retinal).

Transduction of Light

The biochemical transformation of absorbed light energy into electrical signals initiated when a photon isomerizes a visual pigment molecule, triggering a biochemical cascade.

Vertical Transmission (Retina)

The straight-through retinal signaling pathway through which photoreceptors transmit signals directly to bipolar cells, which in turn synapse onto ganglion cells.

Horizontal Cells

Retinal interneurons that mediate lateral transmission of signals horizontally across photoreceptors.

Amacrine Cells

Retinal interneurons that transmit signals horizontally across bipolar cells and across ganglion cells.

Neural Convergence

The wiring pattern where multiple photoreceptors funnel onto a single ganglion cell (averaging $120\text{ rods}$ to $1\text{ ganglion cell}$, compared to a $1\text{ cone}$ to $1\text{ ganglion cell}$ ratio in the fovea).

Visual Acuity

The spatial resolution of the visual processing system (demonstrated by the ability to distinguish a $1.75\,\text{mm}$ gap at a distance of $6\,\text{m}$), which is maximized in the fovea due to low convergence.