The ability to match the intensities of sensations that come from different sensory modalities. This ability enables insight into sensory differences. For example, a listener might adjust the brightness of a light until it matches the loudness of a tone.
just noticeable difference (JND) (or difference threshold)
The smallest detectable difference between two stimuli, or the minimum change in a stimulus that enables it to be correctly judged as different from a reference stimulus.
Stevens’ power law
A principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent.
period or wavelength
The time (or space) required for one cycle of a repeating waveform.
method of adjustment
A method of limits in which the subject controls the change in the stimulus.
oculomotor (III) nerves
The third pair of cranial nerves, which innervate all the extrinsic muscles of the eye except the lateral rectus and the superior oblique muscles, and which innervate the elevator muscle of the upper eyelid, the ciliary muscle, and the sphincter muscle of the pupil.
The ability to detect a stimulus and, perhaps, to turn that detection into a private experience.
functional magnetic resonance imaging (fMRI)
A variant of magnetic resonance imaging that makes it possible to measure localized patterns of activity in the brain. Activated neurons provoke increased blood flow, which can be quantified by measuring changes in of the response of oxygenated and deoxygenated blood to strong magnetic fields.
computed tomography (CT)
An imaging technology that uses X-rays to create images of slices through volumes of material (e.g., the human body).
The principle describing the relationship between stimulus and resulting sensation that says the just noticeable difference (JND) is a constant fraction of the comparison stimulus.
The idea that there is a force in life that is distinct from physical entities.
In signal detection theory, an internal threshold that is set by the observer. If the internal response is above criterion, the observer gives one response (e.g., “yes, I hear that”). Below criterion, the observer gives another response (e.g., “no, I hear nothing”).
An individual whose perception of taste sensations is the most intense.
The minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time.
two-point touch threshold
The minimum distance at which two stimuli (e.g., two simultaneous touches) are just perceptible as separate.
A chemical substance used in neuronal communication at synapses.
A psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli.
(1) In hearing, a waveform for which variation as a function of time is a sine function. Also called pure tone. (2) In vision, a pattern for which variation in a property like brightness or color as a function of space is a sine function.
method of limits
A psychophysical method in which the particular dimension of a stimulus, or the difference between two stimuli, is varied incrementally until the participant responds differently.
The science of defining quantitative relationships between physical and psychological (subjective) events.
abducens (VI) nerves
The sixth pair of cranial nerves, which innervate the lateral rectus muscle of each eye.
The act of giving meaning to a detected sensation.
olfactory (I) nerves
The first pair of cranial nerves. The axons of the olfactory sensory neurons bundle together after passing through the cribriform plate to form the olfactory nerve, which conducts impulses from the olfactory epithelia in the nose to the olfactory bulb.
cycles per degree
The number of pairs of dark and bright bars per degree of visual angle.
The idea that the mind has an existence separate from the material world of the body.
trochlear (IV) nerves
The fourth pair of cranial nerves, which innervate the superior oblique muscles of the eyeballs.
A technique that, using many electrodes on the scalp, measures electrical activity from populations of many neurons in the brain.
The idea that the mind exists as a property of all matter—that is, that all matter has consciousness.
Blending multiple sensory systems.
The constant of proportionality in Weber’s law.
optic (II) nerves
The second pair of cranial nerves, which arise from the retina and carry visual information to the thalamus and other parts of the brain.
receiver operating characteristic (ROC) curve
In studies of signal detection, the graphical plot of the hit rate as a function of the false-alarm rate. If these are the same, points fall on the diagonal, indicating that the observer cannot tell the difference between the presence and absence of the signal. As the observer’s sensitivity increases, the curve bows upward toward the upper left corner. That point represents a perfect ability to distinguish signal from noise (100% hits, 0% false alarms).
A mathematical procedure by which any signal can be separated into component sine waves at different frequencies. Combining these sine waves will reproduce the original signal.
quale (pl. qualia)
In philosophy, a private conscious experience of sensation or perception.
auditory (VIII) nerves
The eighth pair of cranial nerves, which connect the inner ear with the brain, transmitting impulses concerned with hearing and spatial orientation. The auditory nerve is composed of the cochlear nerve branch and the vestibular nerve branch, leading to the alternate name vestibulocochlear nerve.
(1) In vision, the relative position of a grating. (2) In hearing, the relative timing of a sine wave.
In signal detection theory, a value that defines the ease with which an observer can tell the difference between the presence and absence of a stimulus or the difference between stimulus 1 and stimulus 2.
The number of cycles of a grating per unit of visual angle (usually specified in cycles per degree).
blood oxygen level–dependent (BOLD) signal
The ratio of oxygenated to deoxygenated hemoglobin that permits the localization of brain neurons that are most involved in a task.
Twelve pairs of nerves (one for each side of the body) that originate in the brain stem and reach sense organs and muscles through openings in the skull.
The idea that the only thing that exists is matter, and that all things, including the mind and consciousness, are the results of interaction between bits of matter.
A principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity.
The junction between neurons that permits information transfer.
doctrine of specific nerve energies
A doctrine, formulated by Johannes Müller, stating that the nature of a sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated.
method of constant stimuli
A psychophysical method in which many stimuli, ranging from rarely to almost always perceivable (or rarely to almost always perceivably different from a reference stimulus), are presented one at a time. Participants respond to each presentation: “yes/no,” “same/different,” and so on.
event-related potential (ERP)
A measure of electrical activity from a subpopulation of neurons in response to particular stimuli that requires averaging many EEG recordings.
magnetic resonance imaging (MRI)
An imaging technology that uses the responses of atoms to strong magnetic fields to form images of structures like the brain. The method can be adapted to measure activity in the brain, as well (see functional magnetic resonance imaging).
A technique, similar to electroencephalography, that measures changes in magnetic activity across populations of many neurons in the brain.
positron emission tomography (PET)
An imaging technology that enables us to define locations in the brain where neurons are especially active by measuring the metabolism of brain cells using safe radioactive isotopes.
signal detection theory
A psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noise. Measures obtained from a series of presentations are sensitivity (d′) and criterion of the observer.