Sensation & Perception

1. Sensation & Perception • What is the difference?

2. Sensation • Detection of physical energy emitted or reflected by physical objects • Sense organs • eyes, ears, tongue, nose, skin, internal body tissues • Without sensations, we would not experience reality

3. Perception • A set of mental operations that organize sensory input into meaningful patterns • Perception allows us to interpret our sensations and thus reality

4. How many Senses? • Five? • Actual many more

5. The Riddle of Separate Sensations • Sense receptors • specialized cells in the sense organs that convert physical energy from the environment into electrical energy to be transmitted as nerve impulses to the brain

6. Johannes Muller • doctrine of specific nerve energies • Different sensory modalities exist b/c signals received by the sense organs stimulate nerve pathways leading to different brain areas • Because different brain areas are stimulated, different sensations are experienced • Synesthesia • Stimulation of one sense evokes sensation of another

7. Functional Codes • Doctrine doesn’t account for variations within a sense • Seeing gold versus yellow • Functional code account for this • Within a sense certain neurons fire or don’t, fire fast or slowly, or in a pattern to create different sensations

8. Measuring the Senses • Psychophysics • How the physical properties of stimuli are related to our psychological experience of them

9. Absolute thresholds • Smallest quantity of energy that can be reliably detected 50% of time • Very sharp senses • candle flame on a clear, dark night from 30 miles away!)

10. Difference thresholds • just noticeable differences (jnds) • Smallest difference in sensory stimulation that can be detected reliably between two stimuli

11. jnds • The larger, or more intense, stimulus 1 is, the greater the jnd needs to be

12. Signal-detection theory • Theory that accounts for response biases in absolute threshold and difference threshold measurements • An observer’s response in a detection task is divided into a sensory process (which depends on the stimulus’s intensity) and a decision process (which is influenced by the participant’s response bias)

13. Signal-detection theory • A mathematical formula separates estimates of a person’s sensory process and decision process, yielding a predicted value for one’s true sensitivity to a particular stimulus

14. Sensory Adaptation • When stimulation is unchanging or repetitious, sensory receptors “tire” and fire less frequently, resulting in a decline in sensory responsiveness • Sensory adaptation to touch/pressure • (the feel of the clothes on your body) • smell (of one’s perfume or cologne)

15. We rarely adapt to visual stimuli • because our eyes are constantly moving back and forth

16. We never completely adapt • to very intense stimuli (e.g., noxious fumes, intense pain)

17. Sensory deprivation • Absence of normal sensory stimulation • Heron (1957)—visual, auditory, an tactile stimulation was deprived, resulting in disorientation, feelings of edginess and confusion, and many reports of hallucinogenic visions

18. Don’t oversimplify!!— • sensory deprivation may be a form of relaxation for some, but torture for others • it all depends upon the context • meditation/relaxation versus solitary confinement in prison

19. Sensory without Perceiving • Selective attention is necessary to focus on and filter out numerous sensory stimuli from being consciously perceived all at once • “Cocktail party phenomenon”