Chapter 4: Sensation & Perception

Sensation

the process of detecting external events with sense organs and turning those stimuli into neural signals

Perception

involves attending to, organizing, and interpreting stimuli that we sense

Transduction

when specialized receptors transform the physical energy of the outside world into neural impulses

Cochlea

specialized structure in the ear where transduction of sound takes place and sound energy is converted into neural impulses that travel to the hearing centres of the brain

Doctrine of Specific Nerve Energies

first proposed in 1826 by the German physiologist Johannes Muller, the doctrine states that the different senses are separated in the brain

Orienting Response

allows us to quickly shift our attentions to new or altered stimuli

Sensory Adaptation

the reduction of activity in sensory receptors with repeated exposure to stimulus

Psychophysics

the field of study that explores how physical energy such as light and sound and their intensity relate to psychological experience

Absolute Threshold

the minimum amount of energy or quantity of a stimulus required for it to be reliably detected at least 50% of the time it is presented

Difference Threshold

the smallest difference between stimuli that can be reliably detected at least 50% of the time

Just Noticeable Difference

when you actually detect a difference

Weber’s Law

states that the just noticeable difference between two stimuli changes as a proportion of those stimuli

Signal Detection Theory

states that whether a stimulus is perceived depends on both the sensory experience and the judgment made by the subject

Sensory Process

the experimenter presents either a faint stimulus or no stimulus at all

Decision Process

the subject is asked to report whether or not a stimulus was actually presented

Motivational Changes

are likely to affect the decision process - survival value (e.g. Hearing is more amplified when alone in the woods)

Subliminal Perception

perception below the threshold of conscious awareness

Priming

a technique in which previous exposure to a stimulus can influence that individual’s later responses, either to the same stimulus or to one that is related to it

• Used in cognitive studies - a word or image would be shown quickly then a different word or image is shown for a longer period of time (mask), which interferes with the conscious perception of the subliminal stimulus

• Subliminally primed words can activate already existing motivational state but  cannot create a new motivational state

Gestalt Psychology

an approach to perception that emphasizes that “the whole is greater than the sum of its parts”

Figure-ground Principle

that objects or figures in our environment tend to stand out against a background - which figure you see can be dependent on many factors (e.g. what you are motivated to see)

Proximity

we tend to treat two or more objects that are in close proximity to each other as a group

Similarity

visually similar elements are grouped together and perceived as related, regardless of their actual proximity

Continuity

perceptual rules that lines and objects tend to be continuous, rather than abruptly changing direction

CLosure

refers to the tendency to fill in gaps to complete a whole object

Phonetic Reversal

where a word pronounced backwards sounds like another word

Top-down Processing

when our perceptions are influenced by our expectations or by our prior knowledge

Bottom-up Processing

occurs when we perceive individual bits of sensory information (e.g. sounds) and use them to construct a more complex perception (e.g. a message)

Perceptual Set

a filter that influences what aspects of a scene we perceive or pay attention to

Divided Attention

paying attention to more than one stimulus or task at the same time

Selective Attention

involves focusing on one particular event or task

Inattentional Blindness

a failure to notice clearly visible events or objects because attention is directed elsewhere

Light

refers to radiation that occupies a relatively narrow band of the electromagnetic spectrum

Wavelength

the distance between peaks of a wave - differences in wavelength correspond to different colours on the electromagnetic spectrum

Amplitude

the height of a wave - low amplitude waves are seen as dim, high amplitude waves are seen as bright colours

• If a large proportion of the light waves are clustered around one wavelength you will see an intense vivid colour

• If there are a large variety of wavelengths being viewed at the same time the colour will appear to be washed out

Hue

colour of the spectrum

Intensity

brightness

Saturation

colourfulness; the purity of a colour

Sclera

the white, outer surface of the eye

Cornea

the clear layer that covers the front portion of the eye and also contributes to the eye’s ability to focus

Pupil

regulates the amount of light that enters by changing its size; it dilates (expands) to allow more light to enter and constricts (shrinks) to allow less light into the eye

Iris

a round muscle that adjusts the size of the pupil; it also gives the eyes their characteristic colour

Lens

a clear structure that focuses light onto the back of the eye

Accommodation

the process where the lens changes shape to ensure that the light entering the eye is refracted in such a way that it is focused when it reaches the back of the eye

Transduction

the process that stimulates a layer of specialized receptors that convert light into a message that the brain can then interpret when light reaches the back of the eye

• Receptors are part of the retina

Retina

lines the inner surface of the back of the eye and consists of specialized receptors that absorb light and send signals related to the properties of light to the brain

Optic Nerve

a dense bundle of fibres that connect to the brain

Optic Disc

an area on the retina with no photoreceptors

Blind Spot

a space in the retina that lacks photoreceptors

Rods

photoreceptors that occupy peripheral regions of the retina; they are highly sensitive under low light levels

Cones

photoreceptors that are sensitive to the different wavelengths of the light that we perceive as colour

Fovea

the central region of the retina

Dark Adaptation

the process by which the rods and cones become increasingly sensitive to light under low levels of illumination

Trichromatic Theory (or Young-Helmoltz Theory)

maintains that colour vision is determined by three different cone types that are sensitive to short, medium, and long wavelengths of light

Negative Afterimage

a different colour from the one you actually viewed

Opponent-process Theory

states that we perceive colour in terms of opposing pairs - red to green, yellow to blue, and white to black

• Cells that are stimulated by red are inhibited by green, and is this way for all colours (rebound effect)

Colour Blindness

Nearsightedness (myopia)

when the eyeball is slightly elongated, causing the image that the cornea and lens focus on to fall short of the retina

Farsightedness (hyperopia)

when the length of the eye is shorter than normal, causing the image to be focused behind the retina

Laser-assisted in-situ keratomileusis (LASIK)

a surgery where they create a small flap on the surface of the eye and then use a laser to reshape the cornea so that incoming light focuses on the retina to correct the vision

Optic Chiasm

the point at which the optic nerves cross at the midline of the brain

Lateral Geniculate Nucleus

specialized for processing visual information 

Feature Detection Cells

these cells respond selectively to simple and specific aspects of a stimulus, such as angles and edges

Ventral Stream

extends from visual cortex to the lower part of the temporal lobe

• Helps with object recognition 

• Groups of neurons in the temporal lobe gather shape and colour info from different regions of the secondary visual cortex and combine it into a neural representation of an object

• Different categories of objects (tools, animals, instruments, etc) are represented in distinct areas of the anterior temporal lobes

Dorsale Stream

extends from the visual cortex to the parietal lobe

• Extends from the visual cortex in our occipital lobe upwards to the parietal lobe

• Less intuitive function than the ventral stream 

• Damage to the dorsal stream causes issues with depth perception and spatial awareness

Prosopagnosia

an inability to recognize faces or face blindness

Fusiform Face Area (FFA)

brain region that detects faces

Face Pareidolia

seeing faces in art when there aren’t faces

Perceptual Constancy

the ability to perceive objects as having constant shape, size, and colour despite changes in perspective

Shape Constancy

we judge the angle of the object relative to our position

Size Constancy

based on judgements of how close an object is relative to one’s position as well as to the positions of other objects

Colour Constancy

allows us to recognize an object’s colour under varying levels of illumination

Binocular Depth Cues

distance cues that are based on the differing perspectives of both eyes

Convergence

occurs when the eye muscles contract so that both eyes focus on a single object

Retinal Disparity (binocular disparity)

the difference in relative position of an object as seen by both eyes, which provides information to the brain about depth

Stereoscopic Vision

results from overlapping visual fields - helps make decisions involving distance and depth

Monocular Cues

depth cues that we can perceive with only one eye

Accommodation

the lens of your eye curves to allow you to focus on nearby objects

Motion Parallax

a disparity in directions and speeds of objects while you are moving (think background and foreground while looking out the window of a car)