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Sensation

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). Sensation and bottom-up processing. How do we know what is real? Empiricism and epistemology

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Sensation

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  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. Berkeley and the limits of sensations • Distal stimulus • Proximal stimulus

  4. A nativist critique • Kant: Sensations are sorted by pre-existing (innate) categories of space, time, and causality • We cannot help but understand our sensations in terms of these categories.

  5. 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, to tell our brains what is out there? • 3. Transduction and coding • Place or anatomical coding • Temporal coding: Rate and pattern

  6. Psychophysics and thresholds: Scaling and measurement. • How do we measure how strong a stimulus is? • The absolute threshold (Reiz Limen or RL) 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 (the median). • Stimuli below the threshold (limen) are subliminal.

  7. More measures of RL: The tachistoscopic method

  8. Relative thresholds: Scale units • 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

  9. 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.

  10. Sensory adaptation • Receptor fatigue • Habituation • Adaptation and contrast • Overcoming adaptation to see what is really there: The flashlight experiment

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

  12. 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

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

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

  15. 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 cells • Blue photopigment, in 5% of cells • Sensed color depends on which combinations of cones are absorbing light in their photopigments.

  16. 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.

  17. Negative afterimages

  18. 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

  19. Would you like to take a class from this teacher? Strongly Agree 1 2 3 4 5 Strongly Disagree

  20. What do you see?

  21. What do you see?

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