Psychophysics and receptors | 6A: Sensing the environment | Psych/soc

Psychophysics

Psychophysics is a field that quantitatively examines how physical stimuli relate to the sensations and perceptions they evoke. By measuring detection thresholds and discrimination abilities, psychophysics bridges the gap between the external world and our internal experience.

Methods in psychophysics:

Method of limits: Gradually increase or decrease stimulus intensity to find the point at which it becomes just detectable.
Method of adjustment: Participants adjust the stimulus themselves until it reaches the threshold.
Method of constant stimuli: Stimuli of different intensities are presented in random order to determine the detection threshold.

Applications

Sensory research: Enables study of thresholds, leading to improved tools like hearing aids.

Ergonomics and design: Helps ensure devices align with human sensory limits.

Neuroscience: Aids in investigating sensory processing pathways and perceptual disorde

Sensory receptors

Sensory receptors convert external stimuli into neural signals, each type specialized for different modalities:

Electromagnetic receptors

Photoreceptors (rods and cones): Detect light in the retina.
Thermoreceptors: Adapt slowly to temperature changes, with distinct “cold” and “warm” ranges.
Mechanoreceptors:
Function: Activated by pressure or pressure changes (e.g., hearing, touch, balance).
Adaptation rates: Very rapidly adapting (detect changes in velocity) or slowly adapting (detect intensity/duration).
Types:
- Pacinian Corpuscles: Deep dermis or subcutaneous tissue; very rapid adaptation for vibration/deep pressure.
- Meissner’s Corpuscles: In the papillary dermis of non-hairy skin; rapid adaptation for two-point discrimination, light touch, low-frequency vibrations.
- Merkel’s Discs/Tactile Discs: Slowly adapting; found in non-hairy skin (dermal-epidermal junction) and mucosal membranes; detect low-frequency vibrations and vertical indentations.
- Ruffini’s Corpuscles: In dermis and joint capsules; sense stretch and joint rotation.

Chemoreceptors

Function: Detect chemical stimuli.
Examples: Olfactory receptors for smell, gustatory receptors for taste, oxygen sensors in carotid/aortic bodies, pH sensors in the medulla.

Nociceptors

Function: Respond to harmful stimuli that can damage tissue (extreme temperatures, high pressure, etc.).
Types:
- Thermal/mechanical (A-delta fibers): Myelinated; fast-conducting; activated by sharp pain or high pressure.
- Polymodal (C Fibers): Unmyelinated; slower; respond to mechanical, chemical, and extreme temperature stimuli.
- TRP ion channels: Activated by noxious stimuli.
- Inflammatory mediators: Histamine, bradykinin, prostaglandins, etc., can directly or indirectly trigger nociceptors, leading to pain and heightened sensitivity.
- Neurotransmitters: Glutamate, substance P, calcitonin, and somatostatin are commonly released during pain signaling.