Sensory Systems and Perception

Question 1

Sensation

Answer 1

Is the process by which sense organs gather information about the environment and transmit it to the brain for initial processing

Question 2

Perception

Answer 2

Is the process by which the brain selects, organises and interprets sensations

Question 3

Three Basic Principles that apply across all senses

Answer 3

1) There is no one-to-one correspondence between physical and psychological reality
2) Sensation and perception are active, not passive
3) Sensory and perceptual processes reflect the impact of adaptive pressures over the course of evolution

Question 4

Hearing

Answer 4

• Sound waves travel through auditory canal to the eardrum, which in turn sets ossicles in motion, amplifying the sound.
• Outer ear collects and magnifies sounds in air
• Middle ear converts waves of air pressure into movements of tiny bone
• Inner ear transforms these movements into waves in fluid that generate neural signals
• From auditory nerve, sensory info passes through the inferior colliculus in the midbrain and the medical geniculate nucleus of the thalamus on to the auditory cortex in the temporal lobes

Question 5

Vision

Answer 5

Two basic processes occur in the eyes:

1) Light is focused on the retina by the cornea, pupil and lens
2) The retina transduces this visual image into a code that the brain can read
- From optic nerve, visual info travels along two pathways
1) Is superior colliculus in the midbrain, which in humans is particularly involved in eye movements
2) Other is lateral geniculate nucleus in the thalamus and on to the visual cortex `

Question 6

Young-Helmholtz or trichromatic theory

Answer 6

Eye contains 3 types of receptors that are most sensitive to wavelengths experienced as red, green or blue.

Question 7

Opponent-process theory

Answer 7

The colours we experience (and after images we perceive) reflect three antagonistic colour systems- blue-yellow, red-green and black-white system

Question 8

Transduction

Answer 8

Process of converting stimulus information into neural impulses

Question 9

Absolute Threshold

Answer 9

Minimum amount of energy needed for an observer to sense that a stimulus is present

Question 10

Difference threshold

Answer 10

Lowest level stimulation required to sense that a change in stimulation has occurred

Question 11

Sensory adaption

Answer 11

Tendency of sensory systems to respond less to stimuli that continue without change

Question 12

Subliminal perception

Answer 12

Tendency to perceive information outside our conscious awareness

Question 13

Perceptual Organisation

Answer 13

Integrates sensations into percepts, locates them in space and preserves their meaning as the perceiver examines them from different vantage points

Question 14

Perceptual interpretation

Answer 14

Involves generating meaning from sensory experience.
-Lies at intersection of sensation and memory, as the brain interprets current sensations in the light of past experience

Question 15

Bottom Up Processing

Answer 15

Emphasises role of sensory data in shaping perception

Question 16

Top down processing

Answer 16

Emphasises the influence of prior experience on perception

Question 17

Three basic principles that apply across all senses

Answer 17

There is no one-to-one correspondence between physical and psychological reality. Sensation and perception are active not passive and sensory perceptual processes reflect the impact of adaptive pressures over the course of evolution.

Question 18

Transduction

Answer 18

Sensation requires converting energy in the world into internal signals that are psychologically meaningful. The more the brain processes these signals the more meaningful they become. Sensation typically begins with an environmental stimulus, a form of energy capable of exciting the nervous system. We only register a tiny fraction of the energy surrounding us and different species have evolved the capacity to process different types of information.

Question 19

Creating a neural code

Answer 19

Specialised cells in the nervous system (sensory receptors) transform energy in environment into neural impulses that can be interpreted by the brain.
Receptors respond to different forms of energy and generate action potentials in sensory neurons adjacent to them. It reads a neural code - pattern of neural firing- and translates it into a psychologically meaningful language

Question 20

1826 Johannes Muller

Answer 20

Proposed doctrine of specific nerve energies, suggests that whether a neural message is experienced as light, sound, smell, taste or touch results less from differences in stimuli than from the particular neurons excited by them. If cotton ball produces a sensation of burning instead of a light touch, this means that sensory receptors may have been rewired to different neural fibres

Question 21

Revising muller’s doctrine

Answer 21

Psychologists recognise that nature of a sensation depends on pathways in brain that it activates. Electrical stimulation of the primary visual cortex produces visual sensations as surely as shining a light in the eye whereas electrical stimulation of auditory cortex produces sensations experienced as sound. Stimulus may be the same- electrical current- but pathways are different.

Question 22

Coding for intensity and quality of the stimulus

Answer 22

For each sense, brain codes sensory stimulation for intensity and quality.
Neural code for intensity, or strength of a sensation varies by sensory modality but usually involves the number of sensory neurons that fire, the frequency with which they fire or some combination of the two.

Question 23

Absolute Threshold

Answer 23

Even if sensory system has capacity to respond to stimulus, individual may not experience stimulus if too weak.
MINIMUM AMOUNT OF PHYSICAL ENERGY NEEDED FOR AN OBSERVER TO NOTICE A STIMULUS IS CALLED AN ABSOLUTE THRESHOLD.
One way psychologists measure absolute thresholds is by presenting a particular stimulus (light, sound, taste, odour, pressure) at varying intensities and determining level of stimulation necessary for person to detect it about 50% of time.

Question 24

Single Detection Theory

Answer 24

According to single detection theory, sensation is not 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.

Question 25

Assessing Response Bias

Answer 25

To assess researchers present participants with stimuli at low intensities, as in traditional procedure for measuring absolute thresholds but they add trials with no stimulus presented. Some times noise alone enough to lead person to say she heard or saw something because its effect crosses the decision criterion. Participants in signal detection experiments can make two kinds of errors.

1) May respond with a false alarm, reporting stimulus when none was present 2) May fail to report actual stimulus.
- Observer who tends to over report sensations will have high number of hits but also a high number of false alarms. An observer who tends to underreport will have a lower number of hits but also a lower number of false alarms.

Question 26

Factors affecting response bias

Answer 26

Whether person has a low or high response bias for reporting ‘yes’ depends on many factors.

1) Expectations
2) Motivation

Question 27

Difference thresholds

Answer 27

The lowest level of stimulation required to sense that a stimulus is present. tHE DIFFERENCE IN INTENSITY between two stimuli that is necessary to produce a just noticeable difference. such as the difference between two light bulbs of slightly different wattage.

Question 28

Weber’s law

Answer 28

• 1834 German physiologist Ernst Weber recognised not only lack of a one to one relationship between physical and psychological worlds but also the existence of a consistent relationship between them.
• Regardless of magnitude of two stimuli, second must differ from the first by a constant proportion for it to be perceived as different
• 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.
• First to show not only that subjective sensory experience and objective sensory stimulation were related but also that one could be predicted from the other mathematically

Question 29

Fechner’s law

Answer 29

Weber’s brother in law Gustav Fechner, took field further in 1860 with the publication of his elements of psychophysics.
Broadened application of webers law by linking the subjective experience of intensity of stimulation with the actual magnitude of a stimulus
estimate precisely how intensly a person would report experiencing a sensation based on the amount of stimulus energy actually present
Fechner’s law means that people experience only a small percentage of actual increases in stimulus intensity but that this percentage is predictable
Knowing the weber constant and the intensity of the stimulus psychologist can actually predict how strong a persons subjective sensation will be.
Remarkable because demonstrates that aspects of our subjective experience can be predicted mathematically

Question 30

Steven’s power law

Answer 30

Fechner’s law held up for a century but was modified by ss stevens because it did not quite apply to all stimuli and senses. Relationship between perceived pain and stimulus intensity is opposite of most other psychophysical relations. The greater the pain the less additional intensity is required for a jnd.
Sensation bears an orderly, predictable relation to physical stimulation but psychological experience in not a photograph, tape recording or wax impression of external reality

Question 31

Sensory Adaption

Answer 31

Final process shared by all sensory systems is adaption. Walk into crowded restaurant and noise level is overwhelming, yet within few minutes you do not even notice it.
Tendency of sensory receptors to respond less to stimuli that continue without change.
Makes sense from evolutionary perspective.
Constant sensory inputs provide no new information about the environment, so nervous system ignores them.

Question 32

Subliminal perception

Answer 32

Refers to 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. e.G. RESEARCHERS HAVE DEMONSTRATED that participants who were presented faces subliminally were able to remember them upon later re-presentation. Most of research involves priming participants by flashing words or symbols at them for a fraction of a second and then determining the effect this has on the chosen outcome variable

Question 33

The nature of light

Answer 33

Light is just one form of electromagnetic radiation, but it is the form to which eye is sensitive. Mere presence of light as a medium for sensation, have shaped virtually every aspect of our psychology, from the time of day at which we are conscious to the way we choose mating partners (using visual appearance as cue).
Light is useful for tracking prey, avoiding predators and checking out potential mates.
Electromagnetic energy travels in waves characterised by patterned movement, or oscillation.
Different forms of radiation have waves of different lengths or wavelengths

Question 34

Focusing light

Answer 34

Light enters eye through cornea, a tough, transparent tissue covering the front of the eyeball. Under water people cannot see clearly because cornea is constructed to bend light rays travelling through air, not water.

Question 35

The Retina

Answer 35

Eye is like a camera. Has an opening to adjust the amount of incoming light, a lens to focus the light and the equivalent of photosensitive film- the retina. Retina translates light energy from illuminated objects into neural impulses, transforming a pattern of light reflected off objects into psychologically meaningful information.

Question 36

Transforming light into sight

Answer 36

Both rods and cones contain photosensitive pigments that change chemical structure in response to light. Process called bleaching because pigment breaks down when exposed to light. Must be reversed before photoreceptor restored to full sensitivity. Pigment regeneration takes time, which is why people often have to feel for seats in a dark room
Readjusting to light is faster

Question 37

Receptive fields

Answer 37

Once rods and cones have responded to patterns of light, nervous system must somehow convert these patterns into a neural code to allow brain to reconstruct the scene. Process begins with ganglion cells. Each ganglion cell has receptive field (region within which a neuron responds to appropriate stimulation)

Question 38

Neural Pathways

Answer 38

Transduction in eye then starts with the focusing of images onto the retina. When photoreceptors bleach, they excite bipolar cells, which in turn cause ganglion cells with particular receptive fields to fire. The axons from these ganglion cells comprise the optic nerve, which transmits information from the retina to the brain

Question 39

Vision: From eye to brain

Answer 39

Impulses from optic nerve first pass through the optic chiasm where the optic nerve splits. Information from left half of each retina goes to left hemisphere and vice versa.

Question 40

Visual Cortex

Answer 40

From the lateral geniculate nucleus, then visual information travels to the primary visual cortex in the occipital lobes. The primary visual cortex is sometimes called the striate cortex because of its striped appearance; visual pathways outside the striate cortex to which its neurons project are thus called extrastriate cortex (because outside of or extra to striate cortex).

Question 41

Visual cortex interim summary

Answer 41

From the optic nerve, visual information travels along two pathways. One is to the superior colliculus in the midbrain, which in humans is particularly involved in eye movements. The other is to the lateral geniculate nucleus in the thalamus and on to the visual cortex. Feature detectors in the primary visual cortex respond only when stimulation in their receptive field matches a particular pattern or orientation. Beyond, the primary visual cortex, visual information flows along two pathways, the what pathway (involved in determining what an object is) and the ‘where’ pathway involved in locating the object in space, following the movement and guiding movements towards it)

Question 42

Young-helmholtz or trichromatic theory

Answer 42

Two theories together explain what is known about colour vision. According to the young-helmholtz or trichromatic theory, eye contains three types of receptors which are most sensitive to wavelengths experienced as red, green or blue.

Question 43

Opponent-process theory.

Answer 43

According to opponent-process theory the colours we experience (and the after images we percieve) reflect three antagonistic colour systems: a blue-yellow, red-green and black-white system. Trichromatic theory operates at the level of the retina and opponent-process theory at higher neural levels.

Question 44

Perception

Answer 44

Line between sensation and perception is thin. Perception organises a continuous array of sensations into meaningful units. When we speak we use a dozen distinct units of sound

Question 45

Organising sensory experience

Answer 45

Examples of perceptual organisation: Put the book on floor it does not suddenly look like part of the floor, if you walk away from it it does not diminish in size.