Lecture 3 definitions

Question 1

Sensation

Answer 1

Refers to the stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses (transduction) that are sent to the brain

Question 2

Perception

Answer 2

Refers to the active process of organising and identifying the stimulus and giving it meaning. Basically, making “sense” of what our senses tell us

Question 3

Psychophysics

Answer 3

A scientific field relating the physical characteristics of stimuli to sensory capabilities. A stimulus (plural stimuli) refers to any physical entity that transfers energy to sensory organs: e.g., light waves, sound waves, airborne particles (smell), dissolved particles (taste), physical force (touch), temperature (pain). A psychophysics experiment might alter the stimulus intensity to determine the absolute limits of sensitivity and/or apply stimuli at different intensity levels to test the limit at which differences can be detected (discriminability).

Question 4

Absolute threshold

Answer 4

The lowest stimulus intensity at which a stimulus can be detected 50% of the time

Question 5

Psychometric function

Answer 5

Expresses sensory capability (e.g., detection, discrimination) as a function of stimulus intensity. It describes how our perception of behaviour changes in response to different stimuli. Example: visual acuity testing with an eye chart (the person sees symbols of different sizes and has to decide which symbol it is)

Question 6

Intra-individual variability

Answer 6

Sensitivity can fluctuate within an individual as it can be influenced by fatigue, expectation or the significance of stimulus to the respondent

Question 7

Inter-individual variability

Answer 7

Individuals can have different decision criteria: how certain do they need to feel before reporting that they detect a stimulus?

Question 8

Discriminability threshold

Answer 8

Referred to as the Just Noticeable Difference (JND), the difference that can be discriminated around 50% of the time. The relative intensity is important here. For example, it is easier to discriminate a 2 grams difference for 100 gram than for 200 grams objects.

Question 9

Weber’s law

Answer 9

Situation when the JND is directly proportional to the intensity of the stimulus. Weber’s constant (K) can be used to measure the ratio of the difference threshold (JND) delta I to the initial stimulus intensity I => K = Delta I / I

Question 10

Cornea

Answer 10

Place where light enters the eye

Question 11

Pupil

Answer 11

Controls the amount of light entering the eye. The eye contains muscle cells that dilate (widen) or constrict (shrink) the pupil

Question 12

Iris

Answer 12

The pigmented region surrounding the pupil

Question 13

Lens

Answer 13

Elastic structure that becomes thinner to focus on distant objects and thicker to focus on near objects. The lens flips the light rays and projects a reversed image onto the retina at the back of the eye

Question 14

Rods and cones

Answer 14

Two types of sensory cells (photoreceptors) in the retina. Rods are largely colour insensitive, but more sensitive to lower intensities of light (dim light conditions). Cones are sensitive to wavelengths in blue, green or red bands.

Question 15

Ganglion cells

Answer 15

Ganglion cells are a type of specialised cells found in the retina of our eyes. Their function can be explained simply as transmitting visual information from the retina to the brain. Ganglion cells receive signals from rods and cones (photoreceptors cells). Rods and cones detect light and convert it into electrical signals that can be understood by the brain. Ganglion cells gather the electrical signals from the rods and cones and transmit them as a bundled signal through their long, thread-like projections called axons. These axons form the optic nerve, which carries the visual information from the eye to the brain.

Question 16

Fovea

Answer 16

Small area in the centre of the retina that contains a high density of cones but few rods. It represents the centre of the visual field and has the highest visual acuity (ability to see fine detail)

Question 17

Foveation

Answer 17

Process of directing our gaze at something

Question 18

Blind spot

Answer 18

Part where there are no photoreceptors (rods, cones) and the optic nerve leaves the eye

Question 19

Trichromatic theory

Answer 19

Argues that the ratio of red, green and blue cone activity is combined downstream (ganglion cells or later) to represent an intermediate colour. The problem is that this theory does not explain the phenomenon of colour aftereffects.

Question 20

Opponent process theory

Answer 20

Argues that information from both rods and cones are integrated (combined) by three types of ganglion cells. When a photoreceptor is activated for a while, it briefly habituates (reduces firing). When the input is removed, the opponent colour is perceived until these photoreceptors recover. It suggests that our visual system processes colour in pairs of opposing or contrasting signals (such as green/red, blue/yellow and black/white). When we look at the colour red, our visual system does not only detect the presence of red but also simultaneously inhibits or suppresses the perception of green. This opposing relationship between red and green is what creates the vividness and clarity of the colour we see.

Question 21

Bottom-up processing

Answer 21

Refers to how our brain makes sense of the world by analysing incoming sensory information. With bottom-up processing, your brain starts by focusing on basic features of an image (e.g., shapes, colours, lines) and combines these individual elements to form the picture. Bottom-up processing starts with sensory input and works it way up to a complete understanding/interpretation.

Question 22

Top-down processing

Answer 22

Refers to the ways in which existing knowledge, expectations, emotional states, arousal, attention, etc. can bias/influence which bottom-up signals get processed and what representations they are assigned to.

Question 23

Gestalt Theory

Answer 23

Suggests a number of principles by which our brains group and interpret stimuli. Law of similarity: similar objects are grouped together. Law of proximity: objects are grouped together based on their proximity to one another. Law of closure: we tend to fill in gaps in incomplete figures. Law of continuity: we link individual elements together in patterns that make sense, meaning those that match natural patterns.