Chapter 1-2 Important Terms

Terms from the study guide in ASULearn,

Abducens (VI) nerves

Controls eye movement (motor/movement)

Absolute threshold

The minimum intensity of a stimulus that can be detected 50% of the time.

Artificial neural networks

Interconnected processing units inspired by biological neural architectures. These systems learn through experience, mimicking the brain's ability to categorize sensory patterns.

Bayesian models

Statistical models that utilize probability to understand how the brain interprets sensory data.

Bloch’s law

The principle that for very brief flashes, visibility is the product of luminance and duration (L x T = C).

Blood oxygen level–dependent (BOLD) signal

The ratio of oxygenated to deoxygenated blood tracked by fMRI.

Computational model

A formal, quantitative description of how the brain processes sensory information.

Cranial nerves

Twelve pairs of nerves connecting the brain to the body without passing through the spinal cord. They conduct information for sensation, motor behavior, or both via the skull base.

Criterion

The internal decision boundary (beta) an observer uses to decide if a signal is present.

Cross-modality matching

A method where an observer matches the perceived intensity of one sense to another.

Deep neural network (DNN)

A hierarchical neural network with many layers and millions of connections. Represents the modern computational shift toward modeling complex feature extraction, such as object recognition.

Doctrine of specific nerve energies

The principle that the nature of a sensory experience is determined by which nerve pathway is activated. Proposed by Müller; explains why pressing your eye (mechanical) results in seeing light (phosphenes).

Efficient coding models

Models postulating that the brain processes information by maximizing efficiency and reducing redundancy. A specialized subset of computational modeling focusing on optimal information transfer.

Electroencephalography (EEG)

A technique using scalp electrodes to measure the electrical activity of massive populations of neurons.

Event-related potential (ERP)

The average of multiple EEG responses to a specific, repeated stimulus. By averaging trials, we isolate the specific neural response from background noise.

Facial (VII) nerves

Manages facial expressions, tear/saliva secretion, and taste on the front two-thirds of the tongue (Both sensory + motor)

Fechner’s law

A mathematical relationship where psychological sensation increases more slowly than physical intensity (S = k log R). The relationship is logarithmic; physical intensity must increase exponentially for sensation to grow linearly.

Functional magnetic resonance imaging (fMRI)

A non-invasive method measuring brain activity by tracking changes in the BOLD signal.

Glossopharyngeal (IX) nerves

Manages taste on the back third of the tongue, swallowing muscles, and gag reflexes (Both sensory + motor).

Interoception

The process of sensing information from inside the body (e.g., heart rate, temperature). Highlights that the "five senses" model is insufficient to describe human sensory experience.

Just noticeable difference (JND)

The smallest detectable change in a stimulus; also known as the difference threshold.

Magnetic resonance imaging (MRI)

A technique producing high-resolution images of brain anatomy using magnetic fields.

Magnetoencephalography (MEG)

A method that detects the tiny magnetic fields produced by the electrical activity of neurons.

Magnitude estimation

A method where observers assign numerical values to the intensity of their sensory experiences. Used to derive the relationship between physical energy and subjective sensation.

Mathematical model

The use of equations to describe the relationship between sensory input and perceptual output. A quantitative framework essential for the predictive power of computational neuroscience.

Method of adjustment

A psychophysical procedure where the participant directly controls the stimulus intensity.

Method of constant stimuli

A procedure presenting stimuli of various intensities in random order.

Method of limits

A procedure using alternating ascending and descending series of stimulus intensities. The threshold is the average of the crossover points where the observer's response changes.

Neuroimaging

A collection of methods used to visualize the structure or function of the living brain. Includes modalities such as EEG, MEG, MRI, and fMRI.

Neuron

The fundamental biological unit of the nervous system, designed to transmit information. Information flows from the dendrites, through the cell body, and down the axon.

Neurotransmitter

Chemical molecules released at the axon terminal to communicate across a synapse.

Oculomotor (III) nerves

Moves the eye, constricts the pupil, and controls the upper eyelid (Motor).

Olfactory (I) nerves

The first pair of cranial nerves, dedicated exclusively to the sense of smell (Sensory).

Optic (II) nerves

The second pair of cranial nerves, dedicated exclusively to the sense of vision (Sensory)

Perception

The higher-order process of interpreting sensory signals to provide them with meaning.

Polysensory

Pertaining to brain areas that integrate information from multiple sensory modalities. These regions are the site of multisensory integration.

Positron emission tomography (PET)

A neuroimaging modality utilized in the field, though its specific physiological markers are not detailed here. Identified as a standard technique for studying the living brain.

Psychophysics

The quantitative study of the relationship between physical stimuli and subjective experience. Founded by Fechner to scientifically bridge the gap between the material and mental worlds.

Receiver operating characteristic (ROC) curve

A graph plotting "Hits" vs. "False Alarms" across various decision criteria.

Sensation

The initial detection of physical energy by specialized sensory receptors. Provides the raw input about the environment that the brain must interpret.

Sensitivity

The ability to distinguish a signal from background noise, measured as d’ (d-prime). Represented by the separation between "Noise" and "Signal + Noise" distributions.

Sensory integration

The process by which the brain combines signals from different senses (e.g., sight and sound).

Signal detection theory

A framework for understanding perceptual decisions made under conditions of uncertainty. Assumes that every detection task involves distinguishing a signal from constant noise.

Statistical optimization model

A model that uses statistical logic to determine the most likely environmental source of a stimulus.

Stevens’s power law

A law stating that perceived sensation (S) is the physical intensity (I) raised to an exponent (b). S = aI^b. If b> 1, sensation grows faster than the stimulus.

Stimulus onset asynchrony (SOA)

The time interval between the start of one stimulus and the start of a subsequent masking stimulus.

Synapse

The microscopic gap between neurons where chemical communication occurs. Prevents direct electrical contact, allowing for the modulation of signals.

Transduction

The critical process of converting physical energy into neural electrical signals (action potentials).

Trochlear (IV) nerves

Controls specific eye movements (moving the eye downward and inward) (Motor).

Vagus (X) nerves

Controls heart rate, digestion, and autonomic functions of organs in the chest and abdomen (Motor).

Vestibulocochlear (VIII) nerves

Controls hearing and balance (Sensory)

Weber fraction

The constant ratio (K) that defines the JND for a particular sensory modality.

Weber’s law

The principle that the JND is a constant proportion of the stimulus intensity. Formula: A i/ I = k. If I is large, the A i must also be large to be detected.

Absorb

The capture of photons by a surface or molecule, preventing their reflection or transmission.

Accommodation

The dynamic process where the ciliary muscles change the shape of the lens to focus. Allows the eye to maintain a clear image of objects at varying distances.

Age-related macular degeneration

A disease resulting in the progressive breakdown of the macula in the central retina. Specifically destroys high-acuity central vision, leaving peripheral vision intact.

Amacrine cell

Retinal neurons that form a lateral pathway, connecting bipolar and ganglion cells. These cells modulate the vertical flow of information in the retinal circuit.

Aqueous humor

The clear, watery fluid located in the anterior chamber between the cornea and lens. Provides nutrients to ocular structures and maintains the eye's internal pressure.

Astigmatism

A refractive error caused by an unequal curvature of the cornea or lens. Prevents light from focusing to a single point, causing blurred vision across all distances.

Bipolar cell

A retinal neuron that receives input from photoreceptors and passes it to ganglion cells. Serves as a bridge in the vertical pathway of the retina.

Cataract

An opacity or clouding of the lens that interferes with light transmission. Light is scattered, preventing the formation of a sharp image on the retina.

Chromophore

The light-sensitive component of a photopigment molecule (e.g., retinal). Captures the photon to begin the sequence of photoactivation.

Cone

A photoreceptor specialized for daylight (photopic) vision, color, and high acuity. Cones adapt rapidly to darkness but have a higher absolute threshold than rods.

Contrast

The difference in luminance between an object and its immediate background. The visual system is tuned to detect changes in contrast rather than absolute light levels.

Cornea

The transparent, highly refractive outer window of the eye. Responsible for approximately two-thirds of the eye's total focusing power.

Diffuse bipolar cell

A bipolar cell that pools input from multiple photoreceptors (usually rods). High sensitivity to dim light, but low spatial resolution (acuity).

Diopter

A unit of measure for the refractive power of a lens (1/focal length in meters). Used to prescribe corrective lenses for refractive errors.

Duplex

The "dual-nature" of the retina, which utilizes two distinct systems (rods and cones). Allows us to see across a massive range of luminance, from starlight to sunlight.

Eccentricity

The angular distance from the center of the fovea to a point on the retina. As eccentricity increases, visual acuity sharply declines.

Emmetropia

The condition of a "perfect" eye where light focuses exactly on the retina.

Filter

A medium that selectively absorbs or transmits specific wavelengths of light. Changes the spectral composition of the light reaching the eye.

Focal distance

The distance between the lens and the point where parallel light rays converge. In a functional eye, the focal distance must match the axial length of the eyeball.

Fovea

A small, specialized pit in the central macula containing only densely packed cones. The site of our highest visual acuity and color processing.

Fundus

The interior back surface of the eye, including the retina and optic disc.

Ganglion cell

The final output neurons of the retina whose axons form the optic nerve. These cells translate retinal processing into the language of action potentials.

Graded potential

An electrical signal that varies in magnitude rather than being all-or-nothing. Photoreceptors and bipolar cells use these to signal the intensity of light.

Horizontal cell

Retinal neurons that mediate lateral inhibition between neighboring photoreceptors. Crucial for enhancing contrast and defining the edges of objects.

Hue

The perceptual attribute of "color" (red, green, blue) determined by wavelength.

Hyperopia

Farsightedness; a condition where the eyeball is too short for its refractive power. Light focuses "behind" the retina, making near objects appear blurry.

Hyperpolarization

Sequence: Light onset → cell membrane becomes more negative → neurotransmitter release stops. Photoreceptors are unique; they are inhibited (hyperpolarized) by their stimulus (light).

Image

A representation of an object formed by light rays that have been refracted or reflected.

Inner segment

The part of the rod or cone containing the nucleus and metabolic machinery. Located between the light-capturing outer segment and the synaptic terminal.

Iris

The pigmented muscular ring that expands or contracts to control the pupil. Regulates the amount of light entering the eye, similar to a camera's aperture.

Koniocellular cell

A specific type of ganglion cell found between the M and P layers of the LGN. Part of the specialized parallel pathways in the visual system.

Lateral inhibition

The process by which excited neurons reduce the activity of their neighbors. Mediated by horizontal cells; it is the fundamental mechanism for edge detection.

Lens

The transparent, flexible structure that provides fine-tuning for focus. Changes shape during accommodation to focus on near vs. far objects.

Macula

The central region of the retina responsible for high-resolution vision. Damage here (as in AMD) causes a loss of the ability to read or recognize faces.

Melanopsin

A photopigment found in a small subset of ganglion cells, not rods or cones. Involved in circadian rhythms and pupil light reflexes rather than "seeing" images.

M ganglion cell

A large "magnocellular" cell that prioritizes temporal resolution (motion). High sensitivity to change but poor at resolving fine spatial detail or color.

Midget bipolar cell

A bipolar cell in the fovea that receives input from a single cone. This 1-to-1 "private line" preserves the highest possible spatial resolution.

Myopia

Nearsightedness; a condition where the eyeball is too long for its refractive power. Light focuses in front of the retina, making distant objects appear blurry.

OFF bipolar cell

A bipolar cell that depolarizes when light is removed (or a shadow appears). Part of the dual-channel system for signaling light decrements.

OFF-center cell

A neuron that increases its firing rate when light is removed from the center of its field. Responds most vigorously to a dark spot on a light background.

ON bipolar cell

A bipolar cell that depolarizes in response to an increase in light. Signals the presence of light increments to the ganglion cells.

ON-center cell

A neuron that increases its firing rate when light hits the center of its receptive field. Inhibited when light hits the surrounding area (center-surround antagonism).

Outer segment

The part of the photoreceptor containing the stacks of discs filled with photopigments. The site where photons are actually captured to begin transduction.

P ganglion cell

A small "parvocellular" cell that prioritizes spatial resolution (detail and color). Provides high-acuity information about the shape and color of objects.

Photoactivation

Sequence: Photon capture by chromophore → change in photopigment shape → closure of ion channels. The fundamental chemical event that initiates the neural visual signal.

Photon

The elementary particle and quantum of light; a discrete packet of energy.

Photoreceptor

The specialized neurons (rods and cones) that perform visual transduction. They convert light energy into the "graded potentials" used by the retina.