Sensation and Perception

Question 1

Define Sensation and Perception

Answer 1

Sensation means the stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain.
Perception is the active process of organising and identifying stimulus and giving it meaning.

Question 2

Define psychophysics and explain how it can be used to study stimulus detection and discriminability.

Answer 2

Psychophysics is a scientific field relating the physical characteristics of stimuli to sensory capabilities.
For stimulus detection, it can be used by altering stimulus intensity to determine the absolute level of sensitivity.
for discriminability, it is used to apply stimuli at different intensity levels to test the limit at which differences can be detected.

Question 3

Identify the major components of the eye and visual system and explain their function.

Answer 3

see scheme
Cornes= the place where the light enters
Pupil= adjustable part that controls the amount of light that enters the eye
Iris= pigmented region around the pupil
Lens= elastic structure that becomes thinner to focus on distant objects and thicker to focus on near objects
Retina= the place at the back of the eye where the image is projected reversed by the lens that flips the light rays

Question 4

Explain the difference between rods and cones and explain the role of cones in colour perception.

Answer 4

The rods are colour insensitive but more sensitive to lower intensities of light.
The cones are each sensitive to wavelengths in blue, green and red bands.
The role of cones is explained by the trichromatic theory: the ratio of red, blue and green cone activities is combined downstream to represent an intermediate colour.

Question 5

Describe how the visual system builds object representations from retina to higher-level cortical regions.

Answer 5

Ganglion projections in the optical nerve terminate in the thalamus. Cells from the left visual hemifield project to the right cortical hemisphere and vice versa. Projections cross over to the opposite hemisphere at the optic chiasm. Thalamic cells then relay the optical signal to the primary visual cortex.

Question 6

Contrast bottom-up vs top-down perceptual processing.

Answer 6

Bottom-up processing refers to how our brain constructs perceptions by binding together primitive representations into complex object representations.
Top-down processing refers to the ways in which existing knowledge, expectations, emotions etc, can bias which bottom-up signals get processed, and what representation they are assigned to.

Question 7

Identify and describe the Gestalt principles of visual perception.

Answer 7

Gestalt theory suggests a number of principles by which our brains group and interpret stimuli.
- Law of similarity: similar objects grouped together
- Law of proximity: similar objects grouped together based on their proximity to one another
- Law of closure: tend to fill in the gaps in incomplete figures
- Law of continuity: link individual elements together in patterns that make sense

Question 8

Ganglion cells

Answer 8

receive converging input from the other layer and project their axons to CNS, through the optic nerve

Question 9

Six stages of sensory processing

Answer 9

1. Sensory receptors receive stimulus
2. Receptors translate stimulus properties into nerve impulses
3. Feature detectors analyze stimulus features
4. Stimulus features are reconstructed into neural representations
5. Neural representation is compared with previously stored info in the brain.
6. Matching process results in the recognition and interpretation of the stimulus.