Chapter Five

Sensation and Perception

Perception

What is sensation?

Sensation

• Process by which stimuli are detected, transduced into nerve impulses, and sent to the brain

• How one detects stimuli and nerve impulses• How stimuli are sensed and sent to brain

Perception

What is perception?

Perception

• The process of organizing stimulus input and giving it meaning

• Organization and meaning are given to stimuli• Individual differences are seen

Sensation and Perception

• Information comes in through our senses– our brains interpret this information– You LOOK with your eyes, you SEE with your brain

• Sensation– Stimulus-detection process – Organs translate stimuli into nerve impulses -

TRANSDUCTION • Perception– Organizing & interprets, giving meaning to input

Absolute Threshold

• Intensity at which stimulus can be detected 50% of time • Lower the absolute threshold - Higher the sensitivity

Difference Thresholds

• How much of a change is required to notice a difference depends on the comparison being made.– In darkness a dim light is visible, but that same

light is not noticed in bright sunlight. A soft whisper is noticed in the quiet, but it may take a shout to be heard at a club.

Sensory Processes

Weber’sLaw• JND is proportional to magnitude of stimulus for which comparison is being made • Proportion is called Weber Fraction • Amount of increase needed to make a difference • If you are carrying 2 kg, 1 additional gram will not make a difference • If you carry only 20 grams, 1 gram will make a

difference Weber’s Law states that the JND is a constant proportion, unique to each sensory system.

Weber Fraction

• For weight is about 1/50• For 50 grams need only 1 gram • For 500 grams need 10 grams • Breaks down at very high & low intensities • Holds for most frequently encountered range

Inattentional Blindness

1. Jennifer plays her music very loud while she studies. Upset by how loud the music is, her mother insists Jennifer turn the music down. After 10 minutes, Jennifer's mom asks her daughter once again to please turn down the volume of the music. Jennifer insists she already turned it down although her mother swears it is as loud as it always was. The fact that Jennifer hears the music as softer and her mother experiences the volume as unchanged indicates that, clearly, Jennifer and her mother have .

A. different absolute thresholds

B. different signal detectionC. difference thresholdsD. different tolerance levels

2. A useful application of Weber fractions is that:A. by looking at them, we can tell what the absolute threshold is.B. they minimize the problems associated with false alarms.C. they minimize the problems associated with misses.D. they allow for sensitivity comparisons between the different sense modalities.

3. You have just arrived at the library to study and just as you are starting to read your assignment, a group of students at a nearby table begin a loud conversation. At first, these extra sounds annoy you, but you return to your reading and pretty soon, you are no longer aware of them, even though the students are continuing to talk. This example is most similar to what is known as:

A. a difference threshold. B. an absolute threshold. C. a perceptual set.D. sensory adaptation.

4. The owl and other nocturnal creatures need exceptional vision due to the low levels of light at night when they are hunting for food. Because their ability to survive depends on this keen sense of sight, their retinas contain .A. more cones than rods B. more rods than cones C. cones but no rodsD. rods but no cones

5. In the visual system, negative colour after images demonstrate the operation of:

A. trichromatic processes.B. opponent processes.C. subtractive colour processes. D. red-green and black-white processes.