The Perceptual Process and Visual System

This flashcard set covers the perceptual process, psychophysical methods, neural physiology of the eye, sensory coding, and visual pathways as described in the lecture notes.

Perceptual Process

A 7-step process beginning with external stimuli and ending with behavioral responses, including perception and recognition.

Distal stimulus

The stimulus as it exists in the environment.

Proximal stimulus

The version of a stimulus that occurs when it hits the receptors.

Transduction

The transformation of physical stimulus energy into electrical signals as action potentials that the nervous system can understand.

Principle of transformation

The process of turning environmental energy into perceptions through transduction, also known as bottom-up processing.

Bottom-up processing

Perception that relies solely on the stimulus and its transduction.

Top-down processing

Perception that is impacted by the use of existing knowledge.

Principle of representation

The concept that everything perceived is based on representations of stimuli formed on receptors and nervous system activity rather than direct contact with the stimulus.

Absolute threshold

The minimum amount of stimulus energy present required to be detected by an individual.

Difference threshold

The minimum amount of variance between two stimuli required to detect a difference.

Method of limits

A testing method for absolute threshold where a stimulus is played in an increasing or decreasing manner until detected.

Method of adjustment

A threshold testing method where stimulus intensity is adjusted in a continuous manner.

Method of constant stimuli

A threshold testing method where stimulus intensities are presented in a random, non-continuous order.

Magnitude estimation

A process where an individual assigns a number to a stimulus based on the perceived intensity between two stimuli.

Action potential

An electrical signal that occurs when a nerve cell reaches $40\,mV$ from a resting state of $-70\,mV$, causing the cell to depolarize and activate.

Sensory coding

The process of turning action potentials into meaningful information for the brain by representing various characteristics through neurons.

Specificity coding

A coding process where individual neurons respond to specific stimuli in the environment, also known as 'yoda neurons.'

Population Coding

A process where experiences are represented by the firing pattern across a large number of sensory neurons.

Visible light

Wavelengths on the electromagnetic spectrum ranging from $400-700\,um$ that are visible to the human eye.

Accomodation

The process where the lens changes shape to focus on objects at different positions and distances.

Myopia

Nearsightedness, or the inability to see objects that are far away.

Hyperopia

Farsightedness, or the inability to see objects close up.

Visual Acuity

The detail and clearness of sight, exemplified by measures like $20/20$ vision.

Fovea

The focus point on the retina containing only cones, representing roughly $1\%$ of all cones.

Blind spot

The area on the retina where the optic nerve is located, containing no rods or cones.

Cone

A photoreceptor used for photopic vision and color acuity, containing three types of opsin (red-green-blue).

Rod

A photoreceptor used for scotopic vision (night vision) providing shade acuity and sensitivity to shorter wavelengths like blues and greens.

Isomerization

The change in shape of a visual pigment molecule caused by the absorption of photons via retinol.

Purkinje shift

The phenomenon where yellows and reds are more visible in photopic vision, while blues and greens pop in scotopic vision.

LGN (Lateral Geniculate Nucleus)

A visual area in the thalamus that regulates neural information from the retina and organizes it for the cortex.

Magnocellular Cells

Neurons in layers 1-2 of the LGN responsible for understanding movement.

Parvocellular Cells

Neurons in layers 3-6 of the LGN responsible for understanding object qualities other than movement.

Center-Surround Receptive Field

A specific area of the retina that a single LGN neuron responds to, featuring an excitatory center and inhibitory periphery (or vice-versa).

Simple cortical cells

Feature detectors in the V1 that respond to specific orientations with side-by-side excitatory and inhibitory fields.

Complex Cells

Neurons that respond to a particular orientation combined with a specific direction of movement.

End-Stop Cells

Neurons sensitive to a particular orientation, direction of motion, and specific length and corners.

Cortical Magnification Factor

The allocation of $10\%$ of the V1 to the fovea, resulting in greater detail and acuity for central images.

Selective Rearing

Experience-based plasticity where visual neural responses are shaped by perceptual experience.

Dorsal Pathway

The 'Where or How' pathway from the V1 to the parietal lobe involved in object location, movement, and action.

Ventral Pathway

The 'What' pathway from the V1 to the temporal lobe involved in object identification, shape, size, and color.

Fusiform Face Area

A part of the inferior temporal cortex that responds maximally to faces compared to other objects.

Prosopagnosia

A specific deficit in the ability to recognize faces.

Visual object agnosia

The impairment of the ability to recognize objects.