Chapter 8: Sensation

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Chapter 8 Sensation
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Sensation

• The process by which our sensory receptors and
  nervous system receive and represent stimuli from
  our environment.
• Sensation involves bottom-up processing because
  first, sense receptors detect a stimulus, and
  then the brain integrates the sensory information.

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Perception

• The process of organizing and interpreting
  sensory information, enabling us to recognize
  meaningful objects and events.
• Perception involves top-down processing because
  when we construct perceptions we draw on or
  experience and expectations. This involves
  higher level mental processes conducted in the
  brain.

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Our 5 Senses Seeing, Hearing, Smelling, Tasting,
Touching

• Sensory systems enable organisms to obtain needed
  information.
• Animals sensory abilities suit their survival
  needs.

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Psychophysics

• The study of relationships between the physical
  characteristics of stimuli, such as their
  intensity, and our psychological experience of
  them.
• What stimuli can we detect?
• At what intensity?
• How sensitive are we to changing stimulation?

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Absolute Threshold

• The minimum stimulation needed to detect a
  particular stimulus 50 of the time.
• Absolute threshold for sight Seeing a candle
  flame on a dark night from 30 miles away.
• For smell Smelling a single drop of perfume in a
  3 room house
• For hearing Hearing a ticking watch from about
  20 feet away.
• For taste Tasting about one teaspoon of sugar
  dissolved in 2 gallons of water.
• For touch Feeling the wing of a bee falling on
  the cheek from about 1 cm away.

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Signal Detection Theory

• According to this theory the threshold for
  detecting a signal depends not only on the
  properties of the stimulus itself, such as its
  intensity- the loudness of a sound, for example-
  but also on the level of background stimulation
  (noise), and on the biological and psychological
  characteristics of the perceiver.

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Subliminal Stimulation

• Stimuli that are below ones absolute threshold
  for conscious awareness.
• Can we sense stimuli below our absolute
  thresholds?
• The Answer is Yes. The effects of subliminal
  perception appear to be subtle and to depend on
  very precise experimental conditions.

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Difference Threshold

• Also called just noticeable difference or jnd
• The minimal difference in the magnitude of energy
  needed for people to detect a difference between
  two stimuli.
• Jnds apply to each of our senses they are the
  minimal differences between two stimuli that
  people can reliably detect.

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Webers Law

• The principle that the amount of change in a
  stimulus needed to detect a difference is given
  by a constant ratio or fraction, called a
  constant, of the original stimulus.
• According to this law, the amount you must change
  a stimulus to detect a difference is given by a
  constant fraction or proportion of the original
  stimulus.

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Examples of Webers Constants

• Saltiness of food 1/5 or 20
• Pressure on skin 1/7 or 14
• Loudness of sounds 1/10 or 10
• Odor 1/20 or 5
• Heaviness of weights 1/50 or 2
• Brightness of lights 1/60 or 1.7
• Pitch of sounds 1/333 or .3

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Sensory Adaptation

• The process by which sensory systems adapt to
  constant stimuli by becoming less sensitive to
  them.
• Our sensory systems deal with repeated exposure
  to the same stimuli by becoming less sensitive to
  them.
• Sensory adaptation may not occur when we are
  repeatedly exposed to certain strong stimuli,
  such as the loud wail of a car alarm.