Constructivist theory (Gregory, 1970)

The biggest mark-loser here. Asked about Gregory, candidates write about optic flow, invariants and affordances — all Gibson's Direct Theory (8.1.2). Self-check: if your word is optic flow, invariant or affordance you are on the wrong theory; hypothesis, inference and prior knowledge are the right ones. Mixing the two earns credit under neither.

Candidates give evidence, then add this supports Gregory's theory — asserting the conclusion without saying how, which scores nothing. A justified point has three parts: the evidence, the mechanism (which named part of the theory it shows), and the consequence for the theory. Once the mechanism is spelled out, no 'this supports' line is needed.

Answers swap these three terms; the mark scheme credits each distinct job. The perceptual hypothesis is the best guess itself, formed then tested. Inference is filling in the missing detail. A second trap is the word 'hypothesis': in research methods it is a testable prediction; here it is a rapid, unconscious guess made in an instant.

Sensation and perception are not the same. Sensation is the detection of a stimulus by a sense organ. Perception is the interpretation of what was detected — the finished experience. Sensory input belongs to sensation; the hypothesis, inference and prior knowledge belong to perception. 'The eye sees the object' skips the construction the theory explains.

'Describe the difference' is not two definitions side by side — that leaves the difference implied and scores one mark. The second mark comes from a connective (whereas, in contrast) naming what they differ on. Gregory says the input is incomplete so the brain infers from prior knowledge, whereas Gibson says the light already specifies the world.

On a strength or weakness item, naming the feature is only the first step — examiners flag this every series. 'A weakness is that the evidence is artificial' is a label. The version that scores adds why and so what: illusion studies use flat drawings shown briefly, which means the evidence may not describe normal viewing. Use point, why, consequence.

Students hear 'the brain constructs perception' and wrongly conclude we imagine the world. In fact the hypothesis is constrained by the sensory input — the brain makes the best guess consistent with what the eye supplies. So the guess is usually right. The real weakness is the opposite: if perception were guessing, we would expect more error than occurs.