Psychology: Sensory Adaptation and Perception

Sensory Adaptation

• Sensory adaptation is the process where sensory receptors become less sensitive to constant stimuli over time.
• Proximal stimulus is represented on a relative scale, not an absolute scale.
• Sensitivity changes depending on the intensity of the background environment.
• Contextual influences on perception begin very early in sensory pathways, affecting how stimuli are processed and perceived.

Visual Adaptation

• Ambient light sensitivity changes based on the ambient light level.
• High ambient light decreases sensitivity to prevent overstimulation.
• Low ambient light increases sensitivity to enhance visibility.
• Example: Moving from a dark movie theater to a bright sunny day outside makes it hard to see initially due to high ambient light.

Weber's Law

• The "just noticeable difference" (JND) is the smallest detectable change in a stimulus.
• Formula: ΔI/I = K (where ΔI is the change in stimulus intensity, I is the original stimulus intensity, and K is the Weber fraction).
• Weber fractions vary for each type of sensory perception (e.g., loudness, brightness, heaviness).
• Example: If you are holding a 100g weight, the smallest detectable weight increase (JND) would be around 2g for heaviness.

Auditory Adaptation & Weber's Law 'Near Miss'

• Auditory adaptation is similar to visual adaptation but in the context of sound.
• Sensitivity changes depending on ambient noise levels.
• Weber's Law 'Near Miss' holds true, but with slight deviations under certain conditions (e.g., very low or very high intensities).
• Example: If listening to a constant tone, the ability to detect a change in pitch will depend on the initial pitch and surrounding noise.

Somatosensory Adaptation

• Changes in sensitivity of the somatosensory system (touch) over time with constant stimulation.
• Example: Wearing a watch initially feels noticeable, but after some time, you stop feeling it due to sensory adaptation.

Receptive Fields

• Definition: The specific area of sensory surface to which a neuron responds.
• Perceptual resolution and acuity are inversely related to sensory receptive field size.
• Smaller fields have higher acuity (e.g., fingertips).
• Larger fields have lower acuity (e.g., back).
• Example: The receptive field of a cone in the retina is the area on the retina that responds to light.

Visual Receptive Fields

• Cone receptive fields are areas on the retina that each cone cell responds to.
• Eccentricity: Receptive field size varies with distance from the fovea (center of the retina).
• Retinal ganglion cells have receptive fields where action potentials respond to light stimuli.
• Center-Surround Receptive Fields: Cells respond differently to light in the center versus the periphery of their receptive fields.
• Example: A ganglion cell might be excited by light in the center of its field and inhibited by light in the surrounding area.

Auditory Receptive Fields

• Hair cells in the cochlea respond to specific frequencies of sound.
• Frequency mapping: Different hair cells are tuned to different frequencies, forming a tonotopic map.
• Example: A hair cell might respond best to a 1000 Hz sound frequency.

Somatosensory Receptive Fields

• Mechanoreceptors are sensory receptors in the skin that respond to touch.
• Field size and acuity vary with location on the body, with smaller fields on fingertips and larger fields on the back.