PSYC289 - Unit 4: Sensation and Perception

Sensation

the stimulation of sense organs.

Perception

the selection, organization, and interpretation of sensory input.

Psychophysics

the study of how physical stimuli are translated into psychological experience.

Absolute threshold

the minimum amount of stimulation that an organism can detect. The absolute threshold occurs when stimuli is detected 50% of the time.

Just noticeable difference (JND)

the smallest difference in the amount of stimulation that a specific sense can detect.

Weber's law

states that the size of a just noticeable difference is a constant proportion of the size of the initial stimulus.

§ Ex: adding 0.5lbs to a 10lb backpack is detectable. Adding 0.5lbs to a 20lb backpack is not. 1lb would have to be added to the 20lb backpack for it to be detectable.

Signal-detection theory

proposes that the detection of stimuli involves decision processes as well as sensory processes, which are both influenced by a variety of factors besides stimulus intensity.

Sensory adaptation

a gradual decline in sensitivity due to prolonged stimulation.

Sensory integration

refers to the way the brain receives, organizes, and responds to sensory information from the body and the environment.

What is light?

Light is a form of electromagnetic radiation and visible light is composed of a small spectrum of all wavelengths. Colour is perceived based off of wavelength. Brightness is perceived from amplitude and saturation is perceived from purity. White light is made up of all colours

Cornea

The "window" to the eye, it protects the eye from debris.

Lens

Focuses light rays entering the eye into the retina.

Accommodation of the lens

occurs when lens adjusts itself to allow for focus on different objects.

Iris

The coloured ring of muscle surrounding the pupil.

Pupil

The opening in the centre of the iris that helps regulate the amount of light passing into the rear chamber of the eye

Retina

The neural tissue lining the inside back surface of the eye; it absorbs light, processes images, and sends visual information to the brain.

Fovea

A spot in the retina that contains only cones; visual acuity is greatest at this spot.

Optic disc, optic nerve and blind spot

The optic disc is a place in the retina where the optic nerve fibres exit the eye. There are no receptors where the optic disc is, and it is therefore a blind spot.

Saccades

Are quick, simultaneous movements of both eyes in the same direction that allow us to see in high resolution despite having a narrow high-resolution field of view. Without saccades sensory adaptation would take over and things would start to fade from view.

Cones

specialized visual receptors that play a key role in daylight vision and colour vision.

Rods

specialized visual receptors that play a key role in night vision and peripheral vision.

What is a receptive field?

A receptive field is the region on the retina in which stimuli of rods and cones will activate a neuron. Receptive fields vary in size, shape, and complexity.

How does vision work?

Signals move from receptors to bipolar cells to ganglion cells, which in turn send impulses along the optic nerve. Axons leave the eyes and travel down the optic nerves to the optic chiasm, the point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain. After reaching the optic chiasm, the optic nerve fibres diverge along two pathways. The main pathway projects into the thalamus, the brain's major relay station. Here axons from the retinas synapse in the (LGN) lateral geniculate nucleus. Visual signals are processed in the LGN and then distributed to areas in the occipital lobe that make up the primary visual cortex. The second visual pathway leaving the optic chiasm branches off to an area in the midbrain called the superior colliculus before travelling through the thalamus and on to the occipital lobe.

Feature detectors

neurons that respond selectively to very specific features of more complex stimuli.

How does subtractive color mixing work?

works by removing some wavelengths of light, leaving less light than was originally there

How does additive colour mixing work?

by putting more light in a mixture than any one light

Trichromatic theory of colour vision

holds that the human eye has three types of receptors ("blue", "green, "red") with differing sensitivities to different light wavelengths.

When does colour blindness occur?

When a cone does not function properly.

Opponent process theory of colour vision

holds that colour perception depends on receptors that make antagonistic responses to three pairs of colours.

Complementary colours

pairs of colours that produce grey tones when mixed together.

Afterimage

a visual image that persists after a stimulus is removed.

Reversible figure

a drawing that is compatible with two interpretations that can shift back and forth.

Perceptual set

a readiness to perceive a stimulus in a particular way can greatly affect this subjectivity.

Change blindness

involves the failure to notice a seemingly obvious change in a visual display.

Inattentional blindness

involves the failure to see unexpected visible objects or events in a visual display.

Feature analysis

the process of detecting specific elements in visual input and assembling them into a more complex form.

Bottom-up processing

is when progression is made from individual elements to a whole.

Top-down processing

is when progression is made from a whole to its elements.

What are the six Gestalt principles?

Proximity, Closure, Similarity, Simplicity, Continuity, Figure and Ground.

What is proximity?

Things that are close to one another seem to belong together.

What is closure?

People often group elements to create a sense of closure, or completeness.

What is similarity?

People tend to group stimuli that are similar.

What is simplicity?

People tend to group elements that combine to form a good figure.

What is continuity?

People tend to connect points that result in straight or gently curved lines that create "smooth" paths

What is figure and ground?

Dividing visual displays into figure and ground is a fundamental way in which people organize visual perceptions. The figure is the thing being looked at, and the ground is the background against which it stands.

Binocular depth cues

cues are clues about distance based on the differing views of the two eyes

Retinal disparity

refers to the fact that objects project images to slightly different locations on the right and left retinas, so the right and left eyes see slightly different views of the object.

Convergence

Involves sensing the eyes converging toward each other as they focus on closer objects.

Monocular depth cues

Clues about distance based on the image in either eye alone.

Motion parallax

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

Accommodation

Occurs as an object comes closer, an individual may sense the accommodation (the change in the curvature of the lens) that must occur for the eye to adjust its focus.

Pictorial depth cues

Give clues about distance that can be given in a flat picture.

Linear perspective

A depth cue reflecting the fact that lines converge in the distance.

Texture gradients

Provide information about depth because details are too small to see when they are far away.

Interposition

If an object comes between you and another object, it must be closer to you.

Relative size

Is a cue because closer objects appear larger.

Height in plane

Reflects the fact that distant objects appear higher in a picture.

Shadowing

Makes light and shadow useful in judging distance.

Perceptual constancy

A tendency to experience a stable perception in the face of continually changing sensory input.

Visual illusion

Involves an apparently inexplicable discrepancy between the appearance of a visual stimulus and its physical reality.

Sound waves

Vibrations of molecules.

How are wavelengths of sound described?

In terms of their frequency, measured in cycles per second or hertz (Hz).

What does the amplitude of a sound wave determine?

The loudness of the sound perceived, measured in decibels (dB).

What is the frequency range of human hearing?

Humans can hear between 20 Hz and 20,000 Hz. Their most easily perceived frequency is around 2000 Hz.

What is the rough rule of thumb for the relationship between decibels and perceived loudness?

Perceived loudness doubles about every 6-10 decibels.

What two factors interact to determine perceived loudness?

Amplitude and frequency.

Which frequency range sounds louder to humans at higher decibels compared to 20 Hz or 20,000 Hz?

The 1000 - 5000 Hz frequency range.

How does hearing work?

Sound travels into the pinna of the ear into the auditory canal. The sound waves vibrate the ear drum, which in turn, vibrate the ossicles (the hammer, anvil, and stirrup). This vibrates the cochlea which stimulates the basilar membrane which holds auditory receptors, the hair cells. The hair cells then fire and send information to the brain.

Eardrum

A taut membrane that vibrates in response to sound waves entering the pinna.

Ossicles

Tiny bones in the middle ear composed of the hammer, anvil and stirrup.

Cochlea

A fluid-filled, coiled tunnel that contains the receptors for hearing.

Basilar membrane

Runs the length of the cochlea and holds the auditory receptors called hair cells.

Hair cells

Convert this physical stimulation into neural impulses that are sent to the brain.

What is auditory localization?

The process of determining the location of the sound we hear.

What are the two critical cues for auditory localization?

Intensity (loudness (the head works as a partial sound barrier to enhance this process (the sound shadow))) and timing (which ear receives sound the fastest).

Gustatory system

The sensory system of taste.

What are the physical stimuli for the sense of taste?

Chemical substances that are soluble (dissolvable in water).

Where are gustatory receptors located?

In clusters of taste cells found in the taste buds that line the trenches around papillae on the tongue.

What are the four primary tastes?

Sweet, sour, bitter, and salty. (umami)

What is the pathway of taste signals in the brain?

Taste signals are routed through the thalamus and onto the insular cortex in the frontal lobe.

Olfactory system

The sensory system of smell.

What is unique about the routing of the olfactory system compared to other sensory systems?

Smell is the only sensory system that is not routed through the thalamus before projecting to the cortex.

Where must chemical stimuli be dissolved to be detected by the olfactory system?

They must be dissolved in the mucus located in the nose.

What are the specific receptors for smell called?

Olfactory cilia, which are hair-like structures in the upper nasal passages.

What is the pathway of olfactory information after leaving the olfactory bulb?

It is routed directly to the olfactory cortex in the temporal lobe and other areas of the cortex.

Flavour

A combination of taste, smell, and the tactile sensation of food in one's mouth.

What are the physical stimuli for touch?

mechanical, thermal, and chemical energy impinging on the skin. These stimuli can produce perceptions of tactile stimulation (the pressure of touch against the skin), warmth, cold, and pain.

Skin patches

Specific cells in the nervous system that respond to touch. They are the functional equivalents of receptive fields in vision and vary considerably in size.

Through which structure do touch signals travel before reaching the somatosensory cortex?

The thalamus

A-delta fibres

Involved in pain messages. A fast, myelinated pathway that registers localized pain and relays it to the somatosensory cortex in a fraction of a second. This manifests as sharp, initial pain.

C fibres

Involved in pain messages. A slower, unmyelinated pathway. Conveys the less localized, longer-lasting, aching or burning pain that comes after the initial injury.

Gate-control theory

Holds that incoming pain signals can be blocked in the spinal cord.

Kinesthetic system

Monitors the positions of the various parts of the body.

Joint receptors (Kinesthetic system)

Some receptors reside in the joints, indicating how much they are bending.

Muscle receptors (Kinesthetic system)

Others reside within the muscles, registering their tautness, or extension.

Kinesthetic stimulation pathway

Most kinesthetic stimulation is transmitted to the brain along the same pathway as tactile stimulation.

Vestibular system

Provides the sense of balance, or equilibrium, compensating for changes in the body's position.

How does the vestibular system work?

Any rotational motion of the head is uniquely represented by a combination of fluid flows in the semicircular canals. These shifts in fluid are detected by hair cells similar to those found along the basilar membrane in the cochlea.