Chapter 3 SENSATION AND PERCEPTION WHAT IS SENSATION

WHAT IS SENSATION? � Sensation is the process in which we receive, transform, and

SENSATION � Sensory receptors- Specialized cells that detect sensory stimuli and convert them into

ABSOLUTE THRESHOLDS Sense Stimulus Receptors Threshold Vision Light energy Rods and cones in the

ERNST WEBER 1795 -1878 � Came up with the idea of difference threshold or

WEBER’S LAW � The amount you must change a stimulus to detect a difference

WEBER’S LAW � If you were lifting a 50 lb. weight, you would probably

SIGNAL DETECTION THEORY �Detection of a stimulus depends on these factors �The intensity of

SIGNAL DETECTION THEORY � Physical condition can play a role in Signal Detection �

SENSORY ADAPTATION � The process by which sensory receptors adapt to constant stimuli by

PERCEPTION � Perception- The process by which the brain interprets sensory information, turning it

ATTENTION: DID YOU NOTICE THAT? � Attention is the first step in perception. �

ATTENTION: DID YOU NOTICE THAT? � We pay more attention to stimuli that are

ATTENTION: DID YOU NOTICE THAT? � Repeated exposure may increase attention to particular stimuli.

MODES OF VISUAL PROCESSING: BOTTOM-UP VS. TOP-DOWN � Bottom-up Processing- The brain assembles specific

MODES OF VISUAL PROCESSING: BOTTOM-UP VS. TOP-DOWN � Top-Down Processing- perceiving patterns as meaningful

GESTALT LAWS OF GROUPING � People tend to group bits and pieces of sensory

GESTALT LAWS OF GROUPING � Proximity- the principle that objects that are near each

GESTALT LAWS OF GROUPING � Similarity- The principle that objects that are similar will

GESTALT LAWS OF GROUPING � Continuity- The principle that a series of stimuli will

GESTALT LAWS OF GROUPING � Closure- The perceptual principle that people tend to piece

GESTALT LAWS OF GROUPING � Connectedness- The principle that objects positioned together or moving

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Chapter 3 SENSATION AND PERCEPTION

WHAT IS SENSATION? � Sensation is the process in which we receive, transform, and process stimuli from the outside world to create sensory experiences of vision, touch, hearing, taste, smell and so on. � There actually 7 body senses, not just the 5 we normally think of.

SENSATION � Sensory receptors- Specialized cells that detect sensory stimuli and convert them into neural impulses, which the brain uses to create the sensations of our senses. � Absolute Threshold- The smallest amount of a given stimulus a person can sense.

ABSOLUTE THRESHOLDS Sense Stimulus Receptors Threshold Vision Light energy Rods and cones in the eye Flame from a single candle 30 miles away Hearing Sound waves Hair cells in the inner ear Ticking of a watch about 20 ft. away Taste Chemical substances that contact the tongue Taste buds on the tongue One teaspoon of sugar dissolved in 2 gallons of water Smell Chemical substances that enter the nose Receptor cells in the upper nostrils One drop of perfume dispensed in a small house Touch Movement of, or pressure on, the skin Nerve endings in the skin The wing of a bee falling on the cheek from about 1 cm.

ERNST WEBER 1795 -1878 � Came up with the idea of difference threshold or just-noticeable difference. � Difference Threshold- The minimal difference between 2 stimuli that people can reliably detect.

WEBER’S LAW � The amount you must change a stimulus to detect a difference is given by a constant fraction or proportion. � Ex. Weber’s constant for noticing a difference in weight is 1/50 or 2% � If you were lifting a 50 lb. weight, you would probably notice a difference unless the weight were increased or decreased by 2% (1 lb. ).

WEBER’S LAW � If you were lifting a 50 lb. weight, you would probably notice a difference unless the weight were increased or decreased by 2% (1 lb. ). � But, if you were lifting a 200 lb. weight, the weight would have to be increased or reduced by 4 lbs. (2%) to notice a difference.

SIGNAL DETECTION THEORY �Detection of a stimulus depends on these factors �The intensity of the stimulus �The level of background stimulus �Biological and psychological characteristics of the perceiver.

SIGNAL DETECTION THEORY � Physical condition can play a role in Signal Detection � Sense of smell is more dull if your nose is stuffed or if you have a cold. � Alertness levels affect signal detection � Motivation: Walking down a dark alley, staying home alone (notice sounds). � Hunger: Aromas or TV commercials when you haven’t eaten in a while

SENSORY ADAPTATION � The process by which sensory receptors adapt to constant stimuli by becoming less sensitive to them. �Cold swimming water �Wristwatch, ring �Music �Odors ( i. e. , men’s locker room)

PERCEPTION � Perception- The process by which the brain interprets sensory information, turning it into meaningful representations of the external world. � Through perception, our brain attempts to make sense of the mass of sensory stimuli that impinge on our sensory organs.

ATTENTION: DID YOU NOTICE THAT? � Attention is the first step in perception. � Through selective attention you limit your attention to certain stimuli while filtering out other stimuli. � Selective attention prevents you from being flooded with extraneous information.

ATTENTION: DID YOU NOTICE THAT? � We pay more attention to stimuli that are meaningful or emotionally significant. � Motivational states, such as hunger or thirst, play important roles in attention. � When we are hungry, we are more likely than when we’ve just eaten to pay attention to odors wafting out of a restaurant.

ATTENTION: DID YOU NOTICE THAT? � Repeated exposure may increase attention to particular stimuli. � On the other hand, exposure to a constant stimulus can lead us to become habituated, or accustomed, to a stimulus. � Ex. The humming sound of an air conditioner

MODES OF VISUAL PROCESSING: BOTTOM-UP VS. TOP-DOWN � Bottom-up Processing- The brain assembles specific features of shapes, such as angles and lines, to form patterns that we can compare with stored images we have seen before. � Bottom-up processing may also be used to combine the individual elements of letters and words into recognizable patterns.

MODES OF VISUAL PROCESSING: BOTTOM-UP VS. TOP-DOWN � Top-Down Processing- perceiving patterns as meaningful wholes- such as recognizing faces of people we knowwithout needing to piece together their components. � Top-down is based on acquired experience and knowledge with patterns, but it is not perfect.

GESTALT LAWS OF GROUPING � People tend to group bits and pieces of sensory information into unitary forms or wholes. � Gestalt psychologists described several principles of grouping, including proximity, similarity, continuity, closure, and connectedness.

GESTALT LAWS OF GROUPING � Proximity- the principle that objects that are near each other will be perceived as belonging to a common set.

GESTALT LAWS OF GROUPING � Similarity- The principle that objects that are similar will be perceived as belonging to the same group.

GESTALT LAWS OF GROUPING � Continuity- The principle that a series of stimuli will be perceived as representing a unified form.

GESTALT LAWS OF GROUPING � Closure- The perceptual principle that people tend to piece together disconnected bits of information to perceive whole forms.

GESTALT LAWS OF GROUPING � Connectedness- The principle that objects positioned together or moving together will be perceived as belonging to the same group.

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