Sensation and Perception
Psychology · Section 1.4 · 18 study cards
Thresholds and adaptation, vision and hearing, the other senses, Gestalt organisation, depth cues, constancies and what illusions reveal.
Practice this set → Spaced repetition, card by card. No account needed.
Method
Put every item on one side of the line
The organising question for this whole unit is whether a phenomenon belongs to sensation or to perception. Sensation is physical energy, receptors and transduction, and it stops at the point where impulses reach the brain. Perception is organisation and interpretation, and everything there is constructive. Thresholds, adaptation, rods and cones and hair cells sit on the sensation side; Gestalt grouping, depth cues, constancies, perceptual set and illusions sit on the perception side. Sorting an unfamiliar term onto the right side usually gets you most of the way to the answer.
Learn every sense on the same template
- What is the physical stimulus? Light waves, pressure waves, molecules, mechanical force.
- Where is the receptor and what does it transduce? Rods and cones in the retina, hair cells on the basilar membrane, taste receptors, olfactory receptors.
- What pathway carries it, and does it pass through the thalamus? Everything does except smell.
- Which stimulus property maps onto which experience? Wavelength gives hue, intensity gives brightness, frequency gives pitch, amplitude gives loudness.
- What goes wrong, and what does the failure show? Colour blindness, the two deafnesses, the blind spot.
Filling in the same five rows for each sense turns a long chapter into one table you can rebuild under exam conditions.
Two theories are usually both right
Where this unit offers a pair of rival theories, the answer is almost always that each describes a different stage or a different range. Trichromatic theory describes the cones, opponent-process describes the stage after them. Place theory handles high pitches, frequency theory handles low ones, with the volley principle covering the middle. Write the division of labour, not a winner.
Depth cues: close one eye
The fastest way to classify any depth cue under pressure is to ask whether it survives with one eye shut. If it does, it is monocular. Only retinal disparity and convergence fail that test.
Definitions and theorems
Worked example
Examine the following description. Standing at the end of a long corridor, a student sees a friend approaching. As the friend walks nearer, the image she casts on the student's retina grows steadily larger, yet the student perceives her as staying the same size. The student also perceives her as nearer than the noticeboards she passes in front of, and recognises her face instantly even though only part of it is visible behind a passing trolley. Name the perceptual phenomenon in each of the three observations, classify the depth cues at work as binocular or monocular, and explain what the first observation shows about perception.
First observation. The retinal image enlarges while the perceived person does not. This is size constancy, one of the perceptual constancies, and it shows that perception is not a direct readout of the retinal image.
Say what constancy requires. The system must be using distance information to correct the changing retinal size. Size perception and distance perception are computed together, which is precisely why supplying false distance cues creates size illusions.
Second observation. Seeing the friend as in front of the noticeboards is interposition, since a nearer object blocks part of a farther one. The corridor itself supplies linear perspective and a texture gradient, and her growing size supplies relative size.
Classify the cues. All four survive with one eye closed, so all four are monocular. Retinal disparity and convergence would also be available at close range, and those two alone are binocular.
Third observation. Recognising a partly hidden face is closure, a Gestalt principle, supported by top-down processing: stored knowledge of what a face looks like completes the fragment.
Draw the conclusion the examiner wants. In all three cases the percept goes beyond the sensory data. Sensation supplied a changing, incomplete image; perception delivered a stable, complete object. That gap is the whole content of this unit.
Common mistakes
- Dropping the 50 percent from threshold definitions. Both the absolute threshold and the difference threshold are defined as detection half of the time, because sensitivity fluctuates. An answer that describes the smallest detectable stimulus without that qualification is marked as incomplete.
- Treating the two colour theories as rivals. They describe successive stages, not competing accounts. Trichromatic explains the cones, opponent-process explains the later neural coding and the afterimage. Choosing one is the error; naming the division of labour is the answer.
- Assigning rods and cones the wrong jobs. Cones need good light and give colour and fine detail, and they crowd the fovea. Rods work in dim light, give no colour, and sit in the periphery. The nightly test is that you see badly and colourlessly in the dark, which is rods doing the work.
- Calling relative size or motion parallax a binocular cue because two eyes are open. The classification is about what the cue requires, not what you happen to be using. Shut one eye: if the cue still works it is monocular, and only retinal disparity and convergence fail.
- Saying subliminal messages can control behaviour. Subliminal stimuli can prime a related idea briefly under laboratory conditions. They cannot persuade, and the commercial claims were fabricated. Exams reward the distinction between weak, fleeting priming and behavioural persuasion.
Practice it
Reading the method is not the same as being able to recall it under pressure. This set drills 18 cards one at a time and schedules each card separately, so the ones you keep missing come back sooner.