Sensation and Perception Flashcards
Transduction
The process of converting physical energy or stimulus information into neural impulses is called transduction.
The brain then interprets the impulses that sensory receptors generate as light, sound, smell, taste, touch or motion. It reads a neural code — a pattern of neural firing — and translates it into a psychologically meaningful ‘language’.
Sensory Receptors
all sensory systems have specialised cells called sensory receptors that respond to environmental stimuli and typically generate action potentials in adjacent sensory neurons.
Absolute Threshold
The minimum amount of physical energy needed for an observer to notice a stimulus is called an absolute threshold.
These thresholds are often idiosyncratic and can vary contextually.
Sensation Theory
The theory that sensation is not a passive process that occurs when the amount of stimulation exceeds a critical threshold; rather, experiencing a sensation means making a judgement about whether a stimulus is present or absent.
According to signal detection theory, two distinct processes are at work in detection tasks. The first is an initial sensory process, reflecting the observer’s sensitivity to the stimulus — how well the person sees, hears or feels the stimulus. The second is a decision process, reflecting the observer’s response bias (or decision criterion) — that is, the individual’s readiness to report detecting a stimulus when uncertain.
Factors Affecting Response Bias
Expectation and Motivation
Difference Threshold
The lowest level 212 Psychology of stimulation required to sense a change in stimulation.
the difference in intensity between two stimuli that is necessary to produce a just noticeable difference (or jnd).
Weber’s Law
That constant proportion — the ratio of change in intensity required to produce a jnd compared to the previous intensity of the stimulus — can be expressed as a fraction, called the Weber fraction.
Heaviness: 1/50
Sound around middle c: 1/10.
Fechner’s Law
The magnitude of a stimulus grows logarithmically as the subjective experience of intensity grows arithmetically, so that people subjectively experience only a fraction of actual increases in stimulation.
He recognised that at low stimulus intensities, only tiny increases in stimulation are required to produce subjective effects as large as those produced by enormous increases in stimulation at high levels of intensity. The result is a logarithmic function, which simply means that as one variable (in this case, subjective intensity) increases arithmetically (1, 2, 3, 4, 5 . . .), the other variable (in this case, objective intensity) increases geometrically (1, 2, 4, 8, 16 . . .).
Stevens’ Power Law
Subjective intensity increases in a linear fashion as actual intensity grows exponentially.
Steven’s recognised that at low stimulus intensities, only tiny increases in stimulation are required to produce subjective effects as large as those produced by enormous increases in stimulation at high levels of intensity. The result is a logarithmic function, which simply means that as one variable (in this case, subjective intensity) increases arithmetically (1, 2, 3, 4, 5 . . .), the other variable (in this case, objective intensity) increases geometrically (1, 2, 4, 8, 16 . . .).
Sensory Adaptation
The tendency of sensory receptors to respond less to stimuli that continue without change.
Subliminal Perception
Refers to a process that occurs outside our conscious awareness — the stimulus passes our absolute threshold but does not cause such a difference that we are able to consciously process it.
The Eye
Two basic processes occur in the eyes. First, the cornea, pupil and lens focus light on the retina. Next, the retina transduces this visual image into neural impulses that are relayed to and interpreted by the brain.
Each anatomical structure has a unique perceptual task and the order in which each structure transduces light is paramount to understanding how the human visual system works in a unified manner.
The Cornea
a tough, transparent tissue covering the front of the eyeball where light enters the eye.
Processing Light in the Eye
From the cornea, light passes through a chamber of fluid called aqueous humour, which supplies oxygen and other nutrients to the cornea and lens. Unlike blood, which performs this function in other parts
of the body, the aqueous humour is a clear fluid, so light can pass through it. Next, light travels through
the pupil, an opening in the centre of the iris (the pigmented tissue that gives the eye its blue, green
or brown colour). Muscle fibres in the iris cause the pupil to expand (dilate) or constrict to regulate the
amount of light entering the eye.
The next step in focusing light occurs in the lens, an elastic, disc-shaped structure about the size of a
lima bean that is involved in focusing the eyes. Muscles attached to cells surrounding the lens alter its
shape to focus on objects at various distances. The lens flattens for distant objects and becomes more
rounded or spherical for closer objects, a process known as accommodation. The light is then projected
through the vitreous humour (a clear, gelatinous liquid) onto the retina, a light-sensitive layer of tissue
at the back of the eye that transduces light into visual sensations. The retina receives a constant flow of
images as people turn their heads and eyes or move through space.
