Textbook Notes (363,452)
Canada (158,372)
Psychology (4,731)
Psychology 1000 (1,558)
Dr.Mike (659)
Chapter 5

Chapter 5.docx

11 Pages
Unlock Document

Western University
Psychology 1000

Chapter 5: Sensation and Perception Sensory and perceptual processes can be distinguished into many steps: 1. Stimulus is received by sensory receptors 2. Receptors translate stimulus properties into nerve impulses (transduction) 3. Feature detectors analyze stimulus features 4. Stimulus features are reconstructed into neural representation 5. Neural representation is compared with previously stored information in brain 6. Matching process results in recognition and interpretation of stimuli Sensation: the stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain Perception: the active process of organizing stimulus input and giving it meaning; making ‘sense’ of what our senses tell us - Perception is an active and creative process; thus, the same sensory input may be perceived in different ways at different times Sensory Processes - Certain neurons have developed into specialized sensory receptors that can transform light waves, sound waves, or other forms of energy into the code language of nerve impulses - There appear to be more than five classical senses with which we are familiar with: o Vision o Audition (hearing) o Touch o Gestation (taste) o Olfaction (smell) - For example, there are senses that provide information about balance and body position - Human sensory systems are designed to extract from the environment the information that we need to function and survive - Psychophysics: the study of relations between the physical characteristics of stimuli and the sensory experiences they evoke; it is concerned with two kinds of sensitivity: o Absolute limits of sensitivity (i.e. what is the softest sound that humans can detect?) o Differences between stimuli (i.e. what is the smallest difference in brightness that we can detect?) Stimulus Detection: The Absolute Threshold - Absolute Threshold: lowest intensity at which a stimulus can be detected correctly 50 percent of the time o The lower the absolute threshold, the greater the sensitivity - The general limits of human sensitivity for the five major senses can be estimated Sense Modality Absolute Threshold Vision Candle flame seen at approximately 50 km on a clear, dark night Hearing Tick of a watch under quiet conditions at approximately six metres Taste 1 teaspoon of sugar in approximately 7.5 litres of water Smell One drop of perfume diffused into the entire volume of a large apartment Touch Wing of a fly or bee falling on your cheek from a distance of one centimeter Signal Detection Theory - At one time, it was assumed that each person had a more or less fixed level of sensitivity for each sense - However, psychologists found out that people’s apparent sensitivity can fluctuate quite a bit o Therefore, the concept of a fixed absolute threshold is inaccurate because there is no single point on the intensity scale that separates non-detection from detection of a stimulus o Instead, there is a range of uncertainty, and people set their own decision criterion  Decision Criterion: a personal standard of certainty before a person will say that they detect a stimulus o Decision criterion can also change depending on such as factors as fatigue, expectation, and the potential significance of the stimulus o Signal Detection Theory: concerned with the factors that influence sensory judgments  In a typical experiment, participants are told that after a warning light appears, a barely perceptible tone may or may not be presented  At low stimulus intensities, both the participants’ and the situation’s characteristics influence the decision criterion  Bold participants have more hits and more false alarms than do conservative participants  Increasing the rewards for hits or the costs for misses results in lower detection thresholds  Navy radar operator may be more likely to notice a faint blip during a wartime mission, when a miss might have disastrous consequences  Physicians who will not perform a risky medical procedure without strong evidence to support their diagnosis, they become more conservative as costs for false alarms are increased (higher detection thresholds) o Signal detection research shows that perception is, in part, a decision The Difference Threshold - Distinguishing between stimuli can sometimes be as important as detecting stimuli in the first place - Difference threshold: the smallest difference between two stimuli that people can perceive 50 percent of the time; also known as just noticeable difference (jnd) - German psychologist Ernst Weber stated that there is some degree of lawfulness in the range of sensitivities within our sensory systems - Weber’s Law: the difference threshold is directly proportional to the magnitude of the stimulus with which the comparison is being made, and be expressed as a Weber fraction (e.g. jnd value for weights is 1/50) o Smaller the fraction, less change is necessary to produce a jnd o Weber’s law breaks down at extremely high and low intensities of stimulation Sensory Modality Weber Fraction Audition (tonal pitch) 1/333 Vision (brightness, white light) 1/60 Kinesthesis (lifted weights) 1/50 Pain (heat produced) 1/30 Audition (loudness) 1/20 Touch (pressure applied to skin) 1/7 Smell (India rubber) 1/4 Taste (salt concentration) 1/3 Sensory Adaptation - Sensory systems are finely attuned to changes in stimulation - Sensory neurons are engineered to respond to a constant stimulus by decreasing their activity - Sensory Adaptation: diminishing sensitivity to an unchanging stimulus - Adaptation, also known as habituation, is a part of everyday experience o It occurs in all sensory modalities - Sensory adaptation may reduce our overall sensitivity, but it frees ours senses from the constant and the mundane to pick up informative changes in the environment (such changes may turn out to be important) The Sensory Systems Vision - The normal stimulus for visions is electromagnetic energy, or light waves, which are measured in nanometers - Our visual system is sensitive only to wavelengths extending from 700 nm (red) down to about 400 nm (blue-violet), which are collectively known as the visual spectrum The Human Eye - Light waves enter the eye through the cornea, a transparent protective structure at the front of the eye - Behind the cornea is the pupil, an adjustable opening that can dilate or constrict to control the amount of light that enters the eye - The pupil’s size is controlled by muscles in the colored iris that surrounds the pupil o Low levels of illumination cause the pupil to dilate o Bright light triggers constriction of the pupil - Behind the pupil is the lens, and elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects o Initially, the lens reverses the image from right to left and top to bottom o Brain reconstructs the visual input into the image that we perceive - Retina is a multi-layered tissue at the rear of the fluid-filled eyeball - Ability to see clearly depends on the lens’s ability to focus the image directly onto the retina o Myopia (nearsightedness): good vision for nearby objects, but difficulty seeing faraway objects; the lens focuses the image in front of the retina  Myopia occurs when the eyeball is longer than normal o Hyperopia (farsightedness): excellent distance vision, but difficulty seeing close up objects; the lens focuses the image behind the retina  Aging typically causes the eyeball to shrink Photoreceptors: The Rods and Cones - Retina, which contains specialized sensory neurons is actually an extension of the brain - It contains two types of light-sensitive receptor cells, called rods and cones o There are about 120 million rods and 6 million cones in the human eye o Rods: function best in dim light, primarily black and white brightness receptors; about 500 times more sensitive to light than are the cones, but do not give rise to color sensations o Cones: color receptors; function best in bright illumination o Humans have both rods and cones  Rods are not found in fovea, a small area in the centre of the retina that contains only cones  Periphery of retina contains mainly rods - Rods and cones send their messages to the brain via two additional layers of cells o Bipolar cells: have synaptic connections with the rod and cones; in turn, they synapse with a layer of about one million ganglion cells o Ganglion cells: axons are collected into a bundle to form optic nerve o Thus, input from more than 126 million rods and cones is eventually funneled into only 1 million traffic lanes leading out of the retina toward higher visual centres o Rods and cones not only form the rear layer of the retina, but their light-sensitive ends actually point away from the direction of the entering light so that they receive only a fraction of the light energy that enters the eye o Visual acuity: ability to see fine detail; results when the visual image projects directly onto the fovea o Blind spot is produced when the optic nerve exits through the back of the eye Visual Transduction: From Light to Nerve Impulses - The process whereby the characteristics of a stimulus are converted into nerve impulses is called transduction - Rods and cones translate light waves into nerve impulses through the action of protein molecules called photopigments o Absorption of light changes the rate of neurotransmitter release o Greater the change in transmitter release, stronger the signal passed on to the optic nerve o The message reaches the thalamus and then on to the visual cortex Brightness Vision and Dark Adaptation - Brightness sensitivity of both the rods and the cones depends in part on the wavelength of the light - Dark Adaptation: progressive improvement in brightness sensitivity that occurs over time under conditions of low illumination o During the process of dark adaptation, the photopigment molecules are regenerated, and the receptor’s sensitivity increases greatly o Cones reach maximum sensitivity in 5 minutes; rods reach maximum sensitivity in 30 minutes Color Vision - Human vision is finely attuned to color - The Trichromatic Theory: advanced by Thomas Young and Hermann von Helmholtz; there are three types of color receptors in the retina o Individual cones are most sensitive to wavelengths that correspond to either blue, green, or red o Each of the receptor classes sends messages to the brain, based on the extent to which they are activated by the light energy’s wavelength o The visual system then combines the signals to recreate the original hue o If all three cones are equally activated, a pure white color is produced  Afterimage: image in a different color appears after a color stimulus has been viewed steadily and then withdrawn - Opponent-process Theory: Ewald Hering also assumed that there are three types of cones; o Proposed that each of the three cone types responds to two different wavelengths o One is red or green, blue or yellow, and black or white - Dual processes in color transduction: combination of trichromatic
More Less

Related notes for Psychology 1000

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.