Sensation

1. Sensation How do we know what is real? Locke and the empiricists: Is sensation where knowledge begins? “The fear of the Lord is the beginning of wisdom.” (Proverbs 1:7)

2. Sensation and bottom-up processing • How do we know what is real? Empiricism and epistemology • Experience is traditionally divided into two parts: • Sensation • Perception • But they are intimately connected. • Sensation is bottom-up; perception is top-down. • Sensation is experienced; perception is constructed.

3. Three parts of the psychology of sensation • 1. Psychophysics: What is the relationship between the physical characteristics of a stimulus and the psychological experience of it? Is it the connection between body and mind, as Fechner thought? • 2. Sensory physiology: How do sense organs, receptor cells, and neural circuits respond to physical stimuli? • 3. Transduction and coding • Place or anatomical coding • Temporal coding: Rate and pattern

4. Psychophysics and thresholds: Scaling. • The absolute threshold (Reiz Limen) in classical psychophysics serves as the zero point. • The absolute threshold is the intensity or duration of a stimulus that is sensed 50% of the time. • Stimuli below the threshold (limen) are subliminal.

5. More measures of Absolute Threshold

6. Relative thresholds • Difference thresholds: Weber, Fechner, and the jnd (just noticeable difference) • Method of limits • Method of right and wrong cases • Method of adjustment • Which is louder? • The Weber fraction: Assignment item 1.

7. Subliminal stimulation • Priming emotions and perceptions are the only reliable effects of subliminal stimulation. • Subliminal stimulation does not increase the likelihood that you will buy a product, vote for a candidate, or break bad habits. • Some people make money by warning against subliminal persuasion. • Some people use subliminal persuasion as an excuse for their own irrational acts.

8. Sensory adaptation • Receptor fatigue • Habituation • Adaptation and contrast: Assignment item 2 • Overcoming adaptation to see what is really there: Assignment item 3.

9. Habituation • Saccadic movement • Stabilizing the retinal image Mounting an LED or a miniature projector on a contact lens produces a fixed retinal image. Sensory adaptation handouts

10. The physics of light • Light energy characteristics • Waves and particles • Frequency: • The visible spectrum: 380nm to 760 nm • Ultraviolet and infrared • Amplitude or intensity • Purity

11. The structure of the eye and the physics of light

12. Physics of light and the visual system • Sensitivity and reliability • Retinal cells • Rods and cones • The fovea • The blind spot • Accommodation • Binocular disparity

13. Color vision • Young & Helmholtz’s trichromatic theory: Different colors are sensed by cones containing different photopigments • Green photopigment, in 50% of cells • Red photopigment, in 45% of cell • Blue photopigment, in 5% of cells • Sensed color depends on which combinations of cones are absorbing light in their photopigments.

14. Opponent process theory • Hering’s theory of ganglion cells • Red/Green cells • Yellow/ Blue cells • Sensed color is coded by rate of firing: Faster for red and yellow; slower for green and blue. • Habituation of ganglion cells produces negative afterimages.

15. Negative afterimages

17. Color Blindness • Sex-linked conditions: Genes on X chromosome, so more common in men. • Protanopia, missing red photopigment • Deuteranopia, missing green photopigment • Non-sex-linked condition • Tritanopia, missing blue photopigment or blue cones

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20. What do you see?

21. What do you see?