Sensation and Perception Notes

Visiting a new country in Europe involves taking in sights and sounds for a sensory experience.
Sensory receptors (vision, hearing, taste, smell, somatosensation) gather information.
The brain filters and processes information to focus on salient details.
This involves sensory processes, neural tracks, and the brain.

Deja vu is a feeling of familiarity in a new place.
It arises from processing information faster than expected.
Exposure to similar stimuli (e.g., movies) can prime deja vu.
It occurs when sensory receptors indicate familiarity, but the memory system doesn't recognize the context.

Sensation and perception are often used interchangeably but have distinct meanings in psychology.
Sensation:
- It aligns with transduction.
- It involves converting physical, electromagnetic, and auditory information into electrical signals.
- Receptors in the peripheral nervous system perform it.
- The stimuli are forwarded to the central nervous system as action potentials and neurotransmitters.
- It is an unfiltered, unprocessed raw signal.
Perception:
- It involves processing information within the central nervous system.
- It helps to make sense of the information significance.
- It includes the external sensory experience and internal brain activities.
- It helps us make sense of the world.
Creating artificial intelligence faces challenges because while robots can sense, teaching them to comprehend and respond is difficult.

Sensory receptors are neurons that respond to stimuli by triggering electrical signals.
Distal stimuli: Physical objects outside the body.
Proximal stimuli: Stimuli that directly interact with sensory receptors.
- Example: Campfire (distal), photons emitted by the fire (proximal).
Sensory receptors encode multiple aspects of a stimulus (e.g., brightness, color, and shape of light).
Psychophysics: The study of the relationship between physical stimuli and the sensations they evoke.
Signals pass through specific sensory pathways to inform the central nervous system.
Transduction occurs via sensory ganglia (collections of neuron cell bodies).
Electrochemical energy is sent along neural pathways to projection areas in the brain for analysis.

Photoreceptors: Respond to electromagnetic waves in the visible spectrum (sight).
Mechanoreceptors: Respond to pressure or movement.
- Hair cells respond to fluid movement in the inner ear (hearing, rotational, and linear acceleration).
Nociceptors: Respond to painful or noxious stimuli (somatosensation).
Thermoreceptors: Respond to changes in temperature (thermosensation).
Osmoreceptors: Respond to the osmolarity of the blood (water hemostasis).
Olfactory receptors: Respond to volatile compounds (smell).
Taste receptors: Respond to dissolved compounds (taste).

Perception is linked to experience and biases, unlike sensation.
Sensory information is sent to the central nervous system as action potentials.
The central nervous system interprets and acts upon action potentials.
The same sensation can produce different perceptions in different people.
Threshold: The minimum amount of a stimulus that renders a difference in perception.
Types of thresholds:
- Absolute threshold
- Threshold of conscious perception
- Difference threshold

The minimum stimulus energy needed to activate a sensory system.
It is a threshold in sensation, not perception.
Below this threshold, stimuli will not be transduced into action potentials.
Examples:
- Sweet taste: A teaspoon of sucrose in two gallons of water.
- Vision: Detecting a candle 30 miles away on a clear, dark night.

Sensory systems can send signals without conscious perception.
The stimulus may be too subtle or brief.
The level of intensity a stimulus must pass to be consciously perceived is the threshold of conscious perception.
Subliminal perception: Information received by the central nervous system but does not cross the threshold.
A stimulus below the absolute threshold will not be transduced.
A stimulus below the threshold of conscious perception reaches the central nervous system but not higher-order brain regions.
There is little practical value in using subliminal perception to sell products.

Also called the just noticeable difference (JND).
It is the minimum change in magnitude required to perceive two stimuli are different.
Below the difference threshold, stimuli seem the same.
Example: Sound waves of 440 Hz and 441 Hz may sound the same.
The just noticeable difference for sound frequency is about 3 Hz.
Psycho physical discrimination testing is used to explore the difference threshold.
Participants report if they perceive a change as the stimulus is varied.
The just noticeable difference is reported as a fraction or percentage rather than absolute differences.
To compute the percentage, divide the change in stimulus by the original stimulus magnitude.
Example: $\frac{3 \text{ Hz}}{440 \text{ Hz}} = 0.0068 = 0.68\%$ .

Ernest Heinrich Weber observed that difference thresholds are proportional and computed as percentages.
Weber's law applies to the perception of loudness, pitch, brightness, and weight.

Perception is affected by nonsensory factors like experiences, memory, motives, and expectations.
Signal detection theory studies how internal and external factors influence thresholds.
Example: How loud someone must yell your name in a crowd depends on environmental, social, psychological, and personality factors.
Basic signal detection experiment:
- Trials in which a signal may or may not be presented.
- Noise trials: Signal is presented.
- Catch trials: Signal is not presented.
- Subjects indicate whether a signal was presented.
Possible outcomes:
- Hit: The signal is presented and correctly perceived.
- Miss: The subject fails to perceive the presented signal.
- False alarm: The subject perceives the signal when it was not presented.
- Correct negative: The subject correctly identifies that no signal was presented.
Tracking rates of these outcomes helps identify factors influencing perception.

The ability to detect a stimulus can change over time through adaptation (physiological and perceptual components).
Examples:
- Pupils dilate in the dark and constrict in the light.
- Muscles in the middle ear dampen vibrations in loud environments.
- Cold water no longer seems so cold.
- We stop feeling clothes on our bodies.
Adaptation focuses attention on relevant stimuli, usually changes in the environment.