Lecture 3 definitions Flashcards
Sensation
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
Perception
Refers to the active process of organising and identifying the stimulus and giving it meaning. Basically, making “sense” of what our senses tell us
Psychophysics
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).
Absolute threshold
The lowest stimulus intensity at which a stimulus can be detected 50% of the time
Psychometric function
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)
Intra-individual variability
Sensitivity can fluctuate within an individual as it can be influenced by fatigue, expectation or the significance of stimulus to the respondent
Inter-individual variability
Individuals can have different decision criteria: how certain do they need to feel before reporting that they detect a stimulus?
Discriminability threshold
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.
Weber’s law
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
Cornea
Place where light enters the eye
Pupil
Controls the amount of light entering the eye. The eye contains muscle cells that dilate (widen) or constrict (shrink) the pupil
Iris
The pigmented region surrounding the pupil
Lens
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
Rods and cones
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.
Ganglion cells
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.
Fovea
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)
Foveation
Process of directing our gaze at something
Blind spot
Part where there are no photoreceptors (rods, cones) and the optic nerve leaves the eye
Trichromatic theory
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.
Opponent process theory
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.
Bottom-up processing
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.
Top-down processing
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.
Gestalt Theory
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.
