QCE Psychology - Unit 3 - Sensation and perception

Sensory pathways: vision and hearing

Trace reception, transduction and transmission through the visual and auditory systems, then explain thalamic and cortical processing.

Part of the free QCE Psychology notes library for Unit 3: Sensation and perception.

Updated 2026-08-08 - 4 min read

Sensation begins when receptors respond to physical energy. Perception organises and interprets the resulting neural activity. Seeing and hearing use different accessory structures and receptors, but both follow the logic of reception, transduction, transmission, preliminary processing and cortical interpretation.

A five-stage framework

| Stage | Vision | Hearing | | --- | --- | --- | | Reception | cornea, pupil and lens direct light to retina | pinna and ear canal direct sound to tympanic membrane | | Transduction | rods and cones convert light into neural signals | cochlear hair cells convert mechanical vibration into neural signals | | Transmission | retinal pathways and optic nerve | auditory nerve | | Preliminary processing | thalamic relay, especially lateral geniculate nucleus | brainstem relays and thalamic medial geniculate nucleus | | Organisation and interpretation | primary visual cortex and wider visual networks | primary auditory cortex and wider auditory networks |

The table is a map, not a complete anatomical description. Processing begins before the cortex and continues through feedback among regions.

Vision from light to organised information

The cornea provides much of the eye's refraction. The pupil controls how much light enters, while the lens changes shape to focus. The retina contains rods, which are highly sensitive in dim light, and cones, which support colour and high-acuity vision.

Photoreceptors do not simply send a pixel copy. Retinal circuits organise contrast and receptive fields before ganglion-cell axons form the optic nerve. At the optic chiasm, some fibres cross, helping each hemisphere process the opposite visual field. Thalamic processing relays and modulates information before the primary visual cortex analyses features such as orientation and location. Wider pathways contribute to object identity and visually guided action.

Hearing from pressure waves to sound qualities

Sound waves vibrate the tympanic membrane. The ossicles transmit and amplify vibration to the cochlea. Movement of cochlear fluid bends hair cells, producing receptor changes. Auditory-nerve firing carries information through brainstem pathways, thalamus and primary auditory cortex.

Three perceptual qualities must be distinguished:

• loudness is strongly related to wave amplitude and perceived intensity
• pitch is strongly related to frequency
• timbre is the quality that distinguishes sounds with similar pitch and loudness, influenced by harmonic composition and temporal pattern

Pitch is not “how high the wave is”; that confuses amplitude and frequency.

Receptive fields and transduction

A receptive field is the region or set of stimulus features that changes a neuron's activity. Receptive fields allow selective coding of contrast, position, frequency or other properties.

Transduction is the conversion of environmental energy into neural activity. Light energy changes photopigments; mechanical vibration bends hair cells. Transmission is the later movement of signals through neural pathways. Examinations often separate these verbs.

Why the thalamus matters—and the smell exception

The thalamus is a major relay and processing hub for sensory information before primary cortical processing. Olfaction is the key syllabus exception: smell is chemical reception and reaches primary olfactory regions without first using the thalamic relay typical of the other senses. Later olfactory processing still interacts with thalamic and cortical systems.

Worked example: localise the disrupted stage

Data and pathway questions

When stimulus data show detection thresholds or response curves:

1. identify the physical variable and psychological measure
2. describe the pattern with values
3. connect it to a receptor or pathway mechanism
4. avoid claiming that a behavioural measure directly records one neuron's activity

A lesion study can associate a pathway with a function, but the conclusion depends on lesion extent, compensatory processing and the validity of the task.

Try it yourself

Common exam traps

• using sensation and perception as synonyms
• calling the lens the main photoreceptor
• saying the auditory nerve carries sound waves rather than neural signals
• confusing amplitude, frequency and timbre
• placing all interpretation in one primary cortex
• saying every sense passes through the thalamus in the same way

Sources

• QCAA Psychology 2025 v1.3 syllabus
• OpenStax Psychology 2e: Sensation versus Perception
• OpenStax Psychology 2e: Hearing
• National Eye Institute: How the eyes work

Finished reading? Practise this topic free

Open Psychology past questions with this Unit 3 topic carried into the question bank, then save your progress for the next review.

Practise this topic free. Free to start. No payment details are required. Exact question coverage depends on the available past-paper syllabus mapping.