Overview of Neuronal Activity and Psychophysics Methods

Single Cell Neuron Recording

Measures response from individual neurons.

Orientationally Sensitive Neurons

Fire action potentials based on light orientation.

Positron Emission Tomography (PET)

Injects radiation to measure brain blood flow.

PET Activation Measurement

Subtracts resting brain activity from task activity.

PET Limitations

Radioactivity, poor temporal and spatial resolution.

Functional Magnetic Resonance Imaging (fMRI)

Measures brain oxygen levels during activity.

fMRI Spatial Resolution

Uses voxels to represent few thousand neurons.

Diffuse Optical Tomography (DOT)

Detects blood oxygen changes via light reflection.

DOT Resolution

Good temporal, poorer spatial resolution than fMRI.

Psychophysics

Studies relationship between stimulus energy and perception.

Absolute Threshold

Minimum intensity needed for sensation detection.

Difference Threshold

Smallest detectable change in stimulus intensity.

Just Noticeable Difference (JND)

Another term for difference threshold.

Methods of Limits

Series of stimulus intensities to find thresholds.

Error of Habituation

Subject may falsely report stimulus detection.

Method of Adjustment

Subject continuously adjusts stimulus intensity.

Method of Constant Stimuli

Uses fixed intensities presented randomly for accuracy.

Staircase Method

Adjusts intensity based on subject's detection responses.

Threshold

Average intensity of stimulus reversals.

Point of Subjective Equality (PSE)

Intensity judged equal to standard half the time.

Point of Objective Equality (POE)

Actual value of the standard stimulus intensity.

Constant Error (CE)

Difference between PSE and POE.

Size-Weight Illusion

Larger object feels lighter despite equal weight.

Psychophysical Scaling

Describes relationships between perception and stimulus intensity.

Weber's Law

JND is a constant proportion of standard intensity.

Weber Fraction (k)

Constant used in JND calculation.

Fechner's Law

Perceived intensity increases slower with higher physical intensity.

Magnitude Estimation

Assigns numbers to stimuli relative to a standard.

Stevens' Law

Describes perception relation for various stimulus modalities.

Receiver Operating Characteristic (ROC) Curve

Graph measuring sensitivity to weak signals.

Neurons

Basic units of the nervous system, approximately 86 billion.

Dendrites

Receive input from other neurons.

Cell Body (Soma)

Contains the nucleus of the neuron.

Axon

Transmits action potentials away from the cell body.

Axon Terminals

Output ends of the neuron, release neurotransmitters.

Signal Detection Theory

Measures sensitivity independent of biases.

Noise

Background stimuli present during signal detection trials.

Neurotransmitters

Chemicals released across synapse to transmit signals.

Action Potential

Electrical impulse traveling down a neuron.

Depolarization

Increase in cell membrane potential due to sodium influx.

Refractory Period

Time after action potential when neuron cannot fire.

Resting Potential

Neuronal voltage at rest, typically -70 mV.

Synaptic Vesicles

Structures that store neurotransmitters for release.

Visual Pathway

Pathway from retina to primary visual cortex.

Optic Chiasm

Point where optic nerves cross, sharing visual info.

Lateral Geniculate Nucleus (LGN)

Thalamic relay center for visual information.

Primary Visual Cortex (V1)

Brain area processing visual information, located in occipital lobe.

Fluorescence

Emission of visible light from UV-absorbing substances.

Rods

Photoreceptors sensitive to low light, low acuity.

Cones

Photoreceptors responsible for color vision, high acuity.

Fovea

Retinal area with highest cone density.

Spatial Acuity

Sharpness of vision; high in cones, low in rods.

Dark Adaptation

Time taken for rods and cones to adjust to darkness.

Spatial Summation

Combining inputs from multiple neurons for increased sensitivity.

Excitatory Synapse

Increases action potential rate in post-synaptic neuron.

Inhibitory Synapse

Decreases action potential rate in post-synaptic neuron.

Lateral Inhibition

Process enhancing contrast by inhibiting surrounding neurons.

Simultaneous Contrast

Perceptual effect where colors appear different due to context.

Mach Bands

Visual illusion enhancing edge perception through lateral inhibition.

Hermann Grid

Illusion created by lateral inhibition, showing ghostly gray squares.

Receptive Field

Area affecting sensory neuron activity.

Ganglion Cells

Retinal cells responding to visual stimuli.

On-center Cell

Excited by light in specific visual area.

Off-center Cell

Inhibited by light in specific visual area.

Center-Surround Antagonism

Retinal receptors inhibit ganglion cell activity.

LGN Cells

Respond best to small light spots.

Cortical Cells

Specialized cells in the visual cortex.

Simple Cells

Respond best to bars of light orientation.

Complex Cells

Respond to light and dark stimuli regardless of location.

Motion Sensitivity

Cells tuned for direction and speed of movement.

Feature Detectors

Cells responding to specific visual features.

Selective Adaptation

Neurons reduce responsiveness after prolonged stimulation.

Neural Fatigue

Decreased firing rate from over-stimulation.

Object Detection

Requires shape assessment from contour edges.

Visual Perception

Involves recognizing changes in the environment.

Retinal Convergence

Multiple receptors connect to a single ganglion cell.

Excitation

Increase in neuron activity due to stimulus.

Inhibition

Decrease in neuron activity due to stimulus.

Edge Detection

Identifying object shape through contour information.

Neural Circuit

Pathway transmitting signals from receptors to brain.

LGN

Lateral geniculate nucleus, visual information relay center.

Layers in LGN

Six layers: 1-2 magnocellular, 3-6 parvocellular.

Magnocellular layers

Layers 1-2, process movement and flickering.

Parvocellular layers

Layers 3-6, process color and form.

Retinotopic mapping

Spatial arrangement of visual stimuli in the brain.

Cortical magnification

Increased detail processing at fixation point.

Ocular dominance columns

Neurons favor input from one eye.

Orientation columns

Neurons respond to specific stimulus orientations.

Location columns

Neurons indicate stimulus location in visual field.

Dorsal pathway

Processes 'where/how' visual information.

Ventral pathway

Processes 'what' visual information.

Parietal cortex

Involved in space perception and motion coordination.

Inferotemporal cortex

Responsible for object recognition.

Area MT

Part of dorsal pathway, involved in motion perception.

V4 neurons

Selective for color and curved edges.

Landmark task

Task assessing spatial awareness in parietal lesions.

Object task

Task assessing object recognition in inferotemporal lesions.

Cells in V1

Respond to straight edges in visual stimuli.

Cells in V4

Respond to contours, combinations of straight edges.

Cells in IT cortex

Respond to shapes, combinations of contours.