Perception and Sensory Memory

Perception and Sensory Memory

First task in describing cognition: to explain how information about the world is processed by our sense organs and the cognitive system.

Physiological aspects of the sense organs are very complex….but they won’t be covered in this course.

Sensation versus Perception


stimulation of the sense organs (see, hear, feel) [things in the world cause physical changes in sense organs]


psychological experience of the world (sort of the end of the process)

In practice, there is no clear dividing line between sensation and perception (as in the eye). One gradually turns into the other. Sensation is the beginning and perception is the ending part.

How many senses are there?


Name Information Receptor Locator
sight/vision visible light eyes (receptors on back of eye)
hearing/audition vibration ears
smell/olfaction odor (gaseous chemicals) nose
taste/gustation soluble substances tongue, soft palate, and nose
touch/haptic senses pressure, temperature, location skin (sensitivity varies)
kinesthetic bodily position and movement muscles and joints
vestibular balance inner ear
organic pressure and pain digestive tract


Limitations: Our sense organs register only a small fraction of what’s in the environment: our eyes can’t “see” infrared or ultraviolet light. It’s possible to measure this but our eyes have not evolved to see them. Our ears cannot hear sounds that animals can hear. It is possible for us to build machines to measure and use forms of energy that we cannot sense (radio waves, X rays).

Research Biases

Most research on sensation and perception concerns vision (>90%).

A distant second is research on audition (~10%).

All the other senses receive relatively little attention (<1%).

Sensitivity of Sense Organs

How bright must a light be to be seen?

How loud must a sound be to be heard?

Explored by 19th century researchers call psychophysicists.


our psychologicial experience of physical stimuli.

assumption: sense organs have fixed and absolute thresholds (limens)

Claim: At some level of intensity, the perception of a stimulus should jump from 0% to 100%. You either perceive it or you don’t. Things we can definitely perceive were called supraliminal. Those things we cannot perceive is calledsubliminal and will never enter into the cognitive system.

Identifying Thresholds

Method of ascending limits

gradually increase intensity of a stimulus until the subject reports awareness of it.  Useful because you can check your work. This would make sure that the threshold holds up.

We can also run experiment in reverse.

Method of descending limits

gradually decrease the intensity of a stimulus until the subject reports it is not long present. Used in conjunction with ascending limits technique, the thresholds should hold up.

They did experiments and found something surprising. Subjects were not always consistent in responding. Inter and Intra subject variability. The researchers figured there had to be some factor that might cause people to behave inconsistently.

Reasons for variability:

(1) errors of anticipation (if you expect to see something, you might see it before you actually do) -responding yes before a stimulus can really be seen – “I think I see it….”

(2) Errors of perseveration – responding yes after a stimulus can no longer be seen (really bright light blinds you in beginning, blinded by a camera flash)

(3) biological variability – name given to phenomenon called random neural firing, interpreted by the brain as sensation. (auditory hallucinations [usually hear own name or something familiar]).  It’s actually very hard not to have perceive things. Total darkness – even when no visual info to process you may see red flashes because of random neural firing.

Conclusion: Sensory thresholds are not fixed and absolute. Assumption was wrong.

Related articles
  • Motivation and Emotion (
  • Wilhelm Wundt and Introspection (
  • Signal Detection Theory (
  • Essentials of Sensation and Perception (

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