Sensation & Perception A.P. Psychology Chapter 4

Drill Read the case of Dr. P….. What accounts for his inability to recognize faces and familiar objects by sight? How would your world be different if you were unable to sense the objects & people around you? Give examples of how your life would change if you were to lose your sense of sight?

Visual Agnosia The inability to recognize objects through sight The person’s eyes function properly, but there seems to be a problem with the processing of what is being seen Seems to be the result of damage somewhere in the visual pathway

Sensation & Perception Sensation The stimulation of the sense organs Involves the absorption of energy, such as light or sound waves by sensory organs Perception The selection, organization, and interpretation of sensory input Involves translating sensation into something that is meaningful

What do you see?

Psychophysics The study of how physical stimuli are translated into psychological experience –Gustav Fechner (1860’s) – German –Sensation begins with a Stimulus »Any detectable input from the environment –Wanted to know - For any given sense, what is the weakest detectable stimulus?

Thresholds Threshold ~ a dividing point between energy levels that do and do not have a detectable effect Absolute Threshold ~ for a specific type of sensory input is the minimum amout of stimulation that an organism can detect Define the boundaries of an organism’s sensory capabilities

Examples of Absolute Thresholds Vision A candle flame seen at 30 miles on a dark clear night Hearing A tick of a watch under quiet conditions at 20 feet Taste One teaspoon of sugar in two gallons of water Smell One drop of perfume diffused into entire the entire volume of a six-room apartment Touch The wing of a fly falling on your cheek from a distance of 1 centimeter

The Just-Noticeable Difference The smallest difference in the amount of stimulation that a specific sense can detect Similar to absolute thresholds – absolute thresholds are the JND from no stimulus input Smallest detectable difference is a fairly stable proportion Ernst Weber Fechner’s brother-in-law First to demonstrate the JND Weber’s Law ~ the size of a JND is a constant proportion of the size of initial stimulus (Weber’s fraction) »Ex. The Weber fraction for lifting weights is approximately 1/30 which means that you should be able to detect the difference between 30 ounce weight & 31 ounce weight, but not a 90 & 91 ounce weight (difference is 3 ounces for 90)

Fechner’s Law States that the magnitude of a sensory experience is proportional to the number of JND’s that the stimulus causing the experience is above the absolute threshold Constant increments in stimulus intensity produce smaller & smaller increases in the perceived magnitude of sensation »Ex. You are in a dark room with a single lamp that has 3 bulbs of the same wattage. You turn a switch and one bulb lights. After a dark room, the difference is striking. Turn again, and a second bulb comes on. The amount of light is doubled, but the room does not seem twice as bright. And so on….

Homework The Secret Life of James Thurber ~ Article & Questions Sensation & Perception Passage