Chapter 8: Sensation

1. Chapter 8: Sensation

2. 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.

3. 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.

4. Our 5 Senses: Seeing, Hearing, Smelling, Tasting, Touching • Sensory systems enable organisms to obtain needed information. • Animals’ sensory abilities suit their survival needs.

5. 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?

6. 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.

7. 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.

8. Subliminal Stimulation • Stimuli that are below one’s 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.

9. 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. • Jnd’s apply to each of our senses… they are the minimal differences between two stimuli that people can reliably detect.

10. Weber’s 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.

11. Examples of Weber’s 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%

12. 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.