Week 5 - Sensation and Perception Part 1

What are sensory receptors?

Specialised cells that detect physical energy and convert it into neural signals. transduction

What is transduction?

Conversion of external physical energy into neural impulses interpretable by the brain.

What is an absolute threshold?

Minimum stimulus intensity detectable 50% of the time.

How do psychophysicists measure absolute threshold?

Present stimuli at varying intensities → record detection → threshold = intensity detected 50% of trials. psychophysics

Difference between absolute threshold and difference threshold?

Absolute = minimum detectable stimulus; difference = minimum detectable change.

What is difference threshold?

The lowest level of stimulation required to sense that a change in stimulation has occured

What is sensory adaptation?

Reduced receptor response to unchanging stimuli; increases sensitivity to change. sensory adaptation

What is visible light?

Electromagnetic wavelengths ~400–700 nm detectable by human photoreceptors.

Where does visible light sit in the electromagnetic spectrum?

Between ultraviolet (shorter) and infrared (longer wavelengths). EM spectrum

What is accommodation in vision?

Lens changes shape (flat for distance, round for near) to focus light on retina.

How does the eye detect light?

Cornea focuses → pupil regulates → lens accommodates → retina transduces via rods & cones → optic nerve → brain.

What do rods do?

Detect low light, movement; no colour; concentrated in periphery.

What do cones do?

Detect colour and fine detail; concentrated in fovea.

Why is peripheral vision poor for detail?

Few cones in periphery; rods converge onto bipolar cells → less precise signals.

What is light adaptation?

Adjusting from dark to bright conditions.

Why do rods adapt slower than cones?

Rod photopigments regenerate slowly (~15 min) vs cones (~5 min). light adaptation

What is a receptive field?

Area of retina where stimulation changes a neuron’s firing.

How does lateral inhibition enhance vision?

Adjacent retinal cells inhibit each other → increases contrast & edge detection.

What is the neural pathway from eye to brain?

 Retina → optic nerve → optic chiasm → LGN (thalamus) → primary visual cortex (V1).

What is the structure of the visual cortex?

V1 (striate cortex) contains feature detectors; extrastriate areas process shape, colour, motion.

What are the three psychological dimensions of colour?

Hue, saturation, lightness.

What does complementary mean in colour?

Colours opposite on colour wheel; when combined, cancel to grey.

Why does mixing blue + yellow light produce grey, but pigments produce green?

Light mixing = additive; pigment mixing = subtractive (pigments absorb wavelengths).

How do afterimages occur?

Fatigue of cone systems → opponent system rebounds with complementary colour.

What is trichromatic theory?

Three cone types (S, M, L) sensitive to blue, green, red wavelengths.

What is opponent-process theory?

 Colour coded in antagonistic pairs: red–green, blue–yellow, black–white.

Are both colour theories valid?

Yes — trichromatic explains retinal processing; opponent‑process explains cortical processing.

What is sound?

Vibrations in air molecules producing pressure waves.

How is sound transmitted?

Vibrations → air pressure waves → ear structures → neural impulses.

What is pitch?

Psychological experience of frequency.

What range can humans hear?

~20 Hz to 20,000 Hz.

What determines loudness?

Amplitude of sound waves.

What unit measures loudness?

Decibels (dB).

How does the ear detect sound?

Pinna → eardrum → ossicles → oval window → cochlear fluid → basilar membrane → hair cells → auditory nerve.

What is place theory?

Different basilar membrane locations respond to different frequencies.

What is frequency theory?

Basilar membrane vibrates at same frequency as sound wave.

Are both pitch theories valid?

Yes — place theory explains high frequencies; frequency theory explains low frequencies.

What is the auditory pathway?

Cochlea → auditory nerve → brainstem → thalamus → auditory cortex.

How do we localise sound?

Intensity differences + timing differences between ears.

How is smell detected?

Gas molecules stimulate receptors in olfactory epithelium → neural impulses.

What is the olfactory pathway?

Olfactory epithelium → olfactory bulb → limbic system + cortex.

How is taste detected?

Molecules in saliva stimulate taste buds → neural impulses via cranial nerves.

How are taste and smell related neurologically?

Both converge in orbitofrontal cortex → flavour perception.

What are skin senses?

Pressure, temperature, pain.

How is pain detected?

Nociceptors → spinal cord → thalamus → cortex.

What is phantom limb?

Pain from missing limb due to cortical remapping.

Why does rubbing a sore toe reduce pain?

Gate control theory — competing signals close pain gate.

What does kinanesthesia detect?

Limb movement and position.

What does the vestibular sense detect?

Balance, gravity, head movement.