Psychology Chapter on Perception

Perception and Sensory Processing

• Increased physical stimulus intensity leads to smaller increases in perceived intensity (psychophysical principle).
• Response expansion occurs when perception increases faster than stimulus intensity, notably in experiences of pain and fear.

Transduction

• Transduction describes how photoreceptors (rods and cones) convert light into electrical signals in the retina.
• Rods are sensitive to low light and essential for night vision.
• Cones are responsible for color vision and visual acuity.

Action Potentials

• An action potential is an electrical signal produced by ion movement (Na+, K+) across a neuron's membrane.
• Resting potential is when a neuron is at rest, typically around -70 mV, with a negative charge inside.
• Sodium (Na⁺) is higher outside the cell, while potassium (K⁺) is concentrated inside; the sodium-potassium pump maintains this balance.

Visual Impairments

• Hyperopia (farsightedness) occurs when the eyeball is too short, making nearby objects difficult to focus on.
• Retinitis Pigmentosa (RP) is a genetic disorder that causes night blindness and peripheral vision loss, eventually leading to tunnel vision or blindness.
• Macular degeneration affects the central retina (macula), causing a loss of central vision while peripheral vision remains intact.

Accommodation

• Accommodation is the lens's ability to change shape, becoming thicker for near objects and thinner for distant objects, enabling focus on the retina.

Parts of the Eye

• The cornea provides most of the eye's focusing power.
• The lens adjusts shape for focused light.
• The retina contains rods and cones for light detection.
• The optic nerve transmits visual information to the brain.

Convergence in Vision

• High convergence is common in rods, enhancing sensitivity to light but reducing acuity.
• Low convergence, particularly in cones (especially in the fovea), leads to higher acuity, beneficial for detail recognition but lower sensitivity in dim light.
• Trade-off: rods favor sensitivity (ideal for night vision) while cones favor acuity (sharp vision in daylight).

Dark and Light Adaptation

• Dark adaptation increases eye sensitivity to low light by regenerating photopigments in rods.
• Light adaptation involves reducing sensitivity during bright light exposure.
• Visual pigment molecules in photoreceptors include opsin and retinal, critical for converting light into electrical signals.

Organization of Retinal Layers

• Five major cell types in the retina: photoreceptors, bipolar cells, ganglion cells, horizontal cells, and amacrine cells.
• The vertical system of the retina processes information by moving signals from photoreceptors to ganglion cells.
• The horizontal system integrates signals across photoreceptors, enhancing contrast through lateral inhibition.

Double Dissociations

• Double dissociations demonstrate that two cognitive functions (e.g., object recognition vs. spatial processing) rely on distinct neural pathways.
• Broca’s Aphasia results from damage to Broca’s area, impairing speech production while comprehension remains intact.
• Wernicke’s Aphasia occurs due to damage to Wernicke’s area, impairing comprehension while leaving speech production intact, albeit nonsensical.

Visual Pathways

• Visual information travels from the retina to the Lateral Geniculate Nucleus (LGN) and then to the Primary Visual Cortex (V1).
• The ventral pathway processes object identity (what), while the dorsal pathway processes spatial location and motion (where/how).