Unit 3: Sensation and Perception

Difference threshold

the minimum difference between any two stimuli that a person can detect 50 percent of the time—has been reached.

Subliminal stimulation

is the receipt of messages that are below one’s absolute threshold for conscious awareness.

signal detection theory

there is no actual absolute threshold because the threshold changes with a variety of factors, including fatigue, attention, expectations, motivation, and emotional distress.

Absolute threshold

the weakest level of a stimulus that can be correctly detected at least half the time.

Sensory adaptation

permits you to focus your attention on informative changes in your environment without being distracted by irrelevant data such as odors or background noises.

Transduction

refers to the transformation of stimulus energy to the electrochemical energy of neural impulses.

Perception

is the process of selecting, organizing, and interpreting sensations, enabling you to recognize meaningful objects and events.

Astigmatism

is caused by an irregularity in the shape of the cornea and/or the lens.

Bipolar cells

Rods and cones both synapse with a second layer of neurons in front of them in your retina.

Dark adaptation

When it suddenly becomes dark, your gradual increase in sensitivity to the low level of light

Blind spot

Where the optic nerve exits the retina, there aren’t any rods or cones, so the part of an image that falls on your retina in that area is missing.

Feature detectors

The thalamus then routes information to the primary visual cortex of your brain, where specific neurons

Parallel processing

Simultaneous processing of stimulus elements

Ewald Hering’s opponent-process theory

certain neurons can be either excited or inhibited, depending on the wavelength of light, and complementary wavelengths have opposite effects.

Hearing

is the primary sensory modality for human language.

Amplitude

is measured in logarithmic units of pressure called decibels (dB).

Pitch

determine the highness or lowness of the sound

sound localization

The process by which you determine the location of a sound

Georg von Békésy’s place theory

the position on the basilar membrane at which waves reach their peak depends on the frequency of a tone.

frequency theory

the rate of the neural impulses traveling up the auditory nerve matches the frequency of a tone, enabling you to sense its pitch.

Conduction deafness

is a loss of hearing that results when the eardrum is punctured or any of the ossicles lose their ability to vibrate.

Nerve (sensorineural) deafness

results from damage to the cochlea, hair cells, or auditory neurons.

Somatosensation

as a general term for four classes of tactile sensations: touch/pressure, warmth, cold, and pain.

Itching

results from repeated gentle stimulation of pain receptors, a tickle results from repeated stimulation of touch receptors, and the sensation of wetness results from simultaneous stimulation of adjacent cold and pressure receptors.

Touch

is necessary for normal development and promotes a sense of well-being.

gate-control theory

Ronald Melzack and Patrick Wall’s ________ attempts to explain the experience of pain.

Kinesthesis

is the system that enables you to sense the position and movement of individual parts of your body.

vestibular sense

is your sense of equilibrium or body orientation.

Gustation (taste) and olfaction (smell)

are called chemical senses because the stimuli are molecules.

Taste receptor cells

are most concentrated not only on your tongue in taste buds embedded in tissue called fungiform papillae, but are also on the roof of your mouth and the opening of your throat.

Tasters

have an average number of taste buds, nontasters have fewer taste buds, and supertasters have the most.

Supertasters

are more sensitive than others to bitter, spicy foods and alcohol, which they find unpleasant.

Bottom-up processing

your sensory receptors detect external stimulation and send these raw data to the brain for analysis.

Selective attention

You focus your awareness on only a limited aspect of all you are capable of experiencing.

Top-down processing

takes what you already know about particular stimulation, what you remember about the context in which it usually appears, and how you label and classify it, to give meaning to your perceptions.

Visual capture

Where you perceive a conflict among senses, vision usually dominates.

phi phenomenon

which is the illusion of movement created by presenting visual stimuli in rapid succession.

Figure–ground relationship

The figure is the dominant object, and the ground is the natural and formless setting for the figure.

Proximity

the nearness of objects to each other, is an organizing principle.

Principle of closure

states that we tend to fill in gaps in patterns.

Principle of similarity

states that like stimuli tend to be perceived as parts of the same pattern.

Principle of continuity

or continuation states that we tend to group stimuli into forms that follow continuous lines or patterns.

Optical or visual illusions

are discrepancies between the appearance of a visual stimulus and its physical reality.

Depth perception

is the ability to judge the distance of objects.

Monocular cues

are clues about distance based on the image of one eye, whereas binocular cues are clues about distance requiring two eyes.

Retinal disparity

which is the slightly different view the two eyes have of the same object because the eyes are a few centimeters apart.

Motion parallax

involves images of objects at different distances moving across the retina at different rates.

Relative size

of familiar objects provides a cue to their distance when the closer of two same-size objects casts a larger image on your retina than the farther one.

Interposition

or overlap can be seen when a closer object cuts off the view of part or all of a more distant one.

Relative clarity

can be seen when closer objects appear sharper than more distant, hazy objects.

Texture gradient

provides a cue to distance when closer objects have a coarser, more distinct texture than faraway objects that appear more densely packed or smooth.

Texture gradient

provides a cue to distance when closer objects have a coarser, more distinct texture than faraway objects that appear more densely packed or smooth.

Relative height

or elevation can be seen when the objects closest to the horizon appear to be the farthest from you.

Linear perspective

provides a cue to distance when parallel lines, such as edges of sidewalks, seem to converge in the distance.

Relative brightness

can be seen when the closer of two identical objects reflects more light to your eyes.

Optical illusions

such as the Müller-Lyer illusion and the Ponzo illusion, in which two identical horizontal bars seems to differ in length, may occur because distance cues lead one line to be judged as farther away than the other.