Study Guides (238,085)
Canada (114,909)
Psychology (1,578)
Dr.Mike (229)

Sensory and Perceptual Processes.docx

10 Pages
Unlock Document

Western University
Psychology 1000

Sensory and Perceptual Processes Sensation- The process by which our sense organs respond to and translate stimuli into nerve impulses sent to the brain Perception- Organizing the stimulus input and giving it meaning Stages of Sensation and Perception  Stimuli activate sensory receptors  Sensory receptors translate information into nerve impulses  Specialized neurons analyze stimuli features  Stimulus pieces are reconstructed and compared to stimuli in memory  Perception is then consciously experienced Psychophysics: Sensitivity to Stimuli  Absolute limits of sensitivity o Dimmest light in which we can see objects o Softest sound we can hear  Recognizing differences between stimuli o Smallest difference in brightness detectable o Recognizing differences between tones Stimulus Detection  The Absolute Threshold o The lowest intensity at which a stimulus can be detected 50% of the time o However, the environment contains a background level of stimulation for each sense and this level (the ADAPTATION level) must be overcome if a stimuli is to be detected o The amount of energy required to overcome the Adaptation level is know as the DIFFERENTIAL THRESHOLD - It is subject to variation with changes in circumstances Locke’s Experiment – Stimulus Detection  Materials: 3 buckets/large bowls  Method: o Fill 1 with very hot water o Fill 1 with very cold water o Fill 1 with tepid water  Procedure: o Subject closes eyes – place one hand in hot and the other in cold for approx. 3 minutes o Then place both hands in tepid water o Ask subject to report sensation for each hand separately o Instruct object to open eyes o Although both hands are in the same water the sensations differ due to prior ADAPTATION Signal Detection Theory  Decision Criterion: A personal standard of certainty before a person will say that they detect a stimulus o Affected by:  Conservativeness or boldness  Increasing rewards for noticing stimuli often results in lower detection thresholds  Increased danger/punishment for noticing stimuli often raises detection threshold o Bold subjects show high hits & high false alarms o Conservative subjects show high misses and correct rejections o However, Criterions can be manipulated by changing the payoff for each cell of the response matric o This shows perception is, to some extent, a decision Subliminal Perception  A subliminal stimulus cannot be perceived consciously but do register in the nervous system o “Subliminal” advertising during a movie (Vicary’s Claim) Subliminal Perception: Research Results  Stimuli above threshold influence behaviors much more than subliminal stimuli  Subliminal stimuli have stronger effects on attitudes  Effects may be due to placebo effects The Difference Threshold – (just noticeable difference or JND) is the smallest difference between two stimuli that people can perceive 50% of the time - Weber’s Law: the JND is directly proportional to the magnitude of the stimulus with which the comparison is made (e.g. 1/50 for weight) Sensory Adaptation (Habituation) - Sensory neurons respond to a constant stimulus by decreasing their activity (the diminishing sensitivity to an unchanging stimulus - Perception of stimuli will decrease if constantly present The Sensory Systems: Vision  The Human Eye o Light enters eye through cornea (transparent protective structure) o Pupil – adjustable opening that dilates or constricts to control amount of light entering o Iris – controls the pupil o Cornea – transparent protective covering o Lens – elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects  Image flipped and reversed onto retina  Ability to see clearly depends on lens’ ability to focus image onto retina  Myopia (nearsightedness) – lens focuses image in front of retina  Hyperopia (farsightedness) – lens focuses image behind retina o Retina – multi layered tissue in rear of eyeball  Optic Disk – a small blind spot with no receptors where the optic nerve exits the eyeball  Photoreceptors: Rods and Cones o Retina is covered in light-sensitive receptor cells o Rods – black and white receptors  Function best in dim light o Cones – color receptors  Function best in bright light  In humans, rods are everywhere except for the fovea (direct center of retina)  Cones decrease in concentration distant from the fovea  Rods and cones send messages to the brain via two additional layers of cells  Bipolar cells have synaptic connections with rods and cones  Bipolar cells synapse with ganglion cells, whose axons form into optic nerve o Cones in the fovea each have private line to a single bipolar cells (unlike others, which have many rods/cones for each bipolar cell)  Visal acuity (ability to see fine detail) increases with image directly on fovea o Blind spot exists at point where ganglion cells exit to form optic nerve  A major source of this condensing is due to the fact that as many as six Rods may be connected to one bipolar cell and several bipolar cells may converge on a single ganglion cell. This process is called LATERAL SUMMATION  This means that signals which originate with Rods have poorer resolution than signals from Cones which are connected 1 to 1 or 2 to 1 with bipolar cells o Transduction – process where characteristics of a stimulus are covered into nerve impulses o Rods and cones accomplish transduction through photo pigments o Absorption of light by photo pigments increase the release of neurotransmitters Steady State Stimulation  When a patch of receptors are in the light and another patch are in the dark rather than transmitting information about every receptor the system sends only information about the boundaries  This process is known as Lateral Inhibition  This occurs because the photoreceptors are linked to higher level cells and those higher level cells are cross linked to one another  Through these cross-links inhibitory signals cancel out the excitatory signals from all receptors except those at the light/dark boundaries. This enhances the boundaries o The enhanced boundaries are known as MACH BANDS o These are very important as they help us to separate figure from background Vision: Eye Movements  3 Major types o Convergence – both eyes look at the same time at the same object o Saccadic – Rapid searching – stationary only briefly o Pursuit – Smooth & continuous tracking  3 Minor movements o Tremors – small muscle fluxations o Drift – failure to hold fixation o Micro saccade – drift correction movement All of these are important as they indicate the retinal image is Not stationary Vision: Dark Adaptation  Dark adaptation – the progressive improvement in brightness sensitivity that occurs over time in low illumination (Photo pigment molecules are regenerated, increasing receptor sensi
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.