Unit 2: How Do Internal and External Factors Influence Behaviour?
Sensation, perception, and states of consciousness
Unit 2 moves from biology to the interface between the person and the environment. Distinguish sensation (detection by sensory receptors) from perception (interpretation). Know Gestalt principles: figure-ground, proximity, similarity, closure, and continuity. Understand depth cues, both binocular (retinal disparity, convergence) and monocular (linear perspective, interposition, relative size, texture gradient). Explain perceptual constancies and distortions such as the Muller-Lyer illusion, and the influence of expectation, context, and culture on perception.
Consciousness is best treated as a continuum: focused attention, daydreaming, alcohol-induced states, and sleep. For sleep, know the stages (N1, N2, N3 slow-wave, REM), typical EEG patterns, and the ultradian rhythm of roughly 90-minute cycles. Explain circadian rhythms and the role of the suprachiasmatic nucleus and melatonin, plus effects of sleep deprivation. For altered states, understand how psychoactive drugs act on neurotransmitters (agonists and antagonists) and the distinction between tolerance, dependence, and withdrawal.
Traps to watch
- Sensation is not perception; questions often describe interpretation and call it sensation.
- REM sleep is not deep sleep; it has high-frequency, low-amplitude activity resembling wakefulness, with muscle atonia.
- Retinal disparity requires two eyes; interposition does not.
- Tolerance is not dependence; tolerance is a reduced response at the same dose.
Rule of thumb
Classify any perceptual cue by asking whether it needs two eyes. If yes, it is binocular; if it works in a photograph, it is monocular.
Worked example
A question describes a person needing more of a drug for the same effect and feeling anxious when stopping. The first part is tolerance; the second is withdrawal, which supports a dependence interpretation.