SensationSensation

How do we know what is real?How do we know what is real?

Locke and the empiricists: Is Locke and the empiricists: Is sensation where sensation where knowledgeknowledge begins? begins?

““The fear of the Lord is the beginning The fear of the Lord is the beginning of of wisdomwisdom.” (Proverbs 1:7).” (Proverbs 1:7)

Sensation and bottom-up Sensation and bottom-up processingprocessing

How do we know what is real? Empiricism and How do we know what is real? Empiricism and epistemologyepistemology

Experience is traditionally divided into two Experience is traditionally divided into two parts: parts: – SensationSensation– PerceptionPerception– But they are intimately connected.But they are intimately connected.– Sensation is bottom-up; perception is top-down.Sensation is bottom-up; perception is top-down.– Sensation is experienced; perception is constructed.Sensation is experienced; perception is constructed.

Three parts of the psychology of Three parts of the psychology of sensationsensation

1. Psychophysics: What is the relationship between the 1. Psychophysics: What is the relationship between the physical characteristics of a stimulus and the physical characteristics of a stimulus and the psychological experience of it? Is it the connection psychological experience of it? Is it the connection between body and mind, as Fechner thought?between body and mind, as Fechner thought?

2. Sensory physiology: How do sense organs, receptor 2. Sensory physiology: How do sense organs, receptor cells, and neural circuits respond to physical stimuli?cells, and neural circuits respond to physical stimuli?

3. Transduction and coding3. Transduction and coding– Place or anatomical codingPlace or anatomical coding– Temporal coding: Rate and patternTemporal coding: Rate and pattern

Psychophysics and thresholds: Psychophysics and thresholds: Scaling.Scaling.

– The absolute threshold (Reiz Limen) in classical The absolute threshold (Reiz Limen) in classical psychophysics serves as the zero point.psychophysics serves as the zero point.

– The absolute threshold is the intensity or duration of a The absolute threshold is the intensity or duration of a stimulus that is sensed 50% of the time.stimulus that is sensed 50% of the time.

– Stimuli below the threshold (limen) are subliminal.Stimuli below the threshold (limen) are subliminal.

More measures of Absolute More measures of Absolute ThresholdThreshold

Relative thresholdsRelative thresholds

Difference thresholds: Weber, Fechner, and Difference thresholds: Weber, Fechner, and the jnd (the jnd (jjust ust nnoticeable oticeable ddifference)ifference)– Method of limitsMethod of limits– Method of right and wrong casesMethod of right and wrong cases– Method of adjustmentMethod of adjustment

Which is louder?Which is louder?

The Weber fraction: Assignment item 1.The Weber fraction: Assignment item 1.

Subliminal stimulationSubliminal stimulation

Priming emotions and perceptions are the only Priming emotions and perceptions are the only reliable effects of subliminal stimulation.reliable effects of subliminal stimulation.

Subliminal stimulation does not increase the Subliminal stimulation does not increase the likelihood that you will buy a product, vote for likelihood that you will buy a product, vote for a candidate, or break bad habits.a candidate, or break bad habits.

Some people make money by warning against Some people make money by warning against subliminal persuasion.subliminal persuasion.

Some people use subliminal persuasion as an Some people use subliminal persuasion as an excuse for their own irrational acts.excuse for their own irrational acts.

Sensory adaptationSensory adaptation

Receptor fatigueReceptor fatigue HabituationHabituation Adaptation and contrast: Assignment item 2Adaptation and contrast: Assignment item 2 Overcoming adaptation to see what is really Overcoming adaptation to see what is really

there: Assignment item 3.there: Assignment item 3.

HabituationHabituation

Saccadic movementSaccadic movement Stabilizing the retinal imageStabilizing the retinal image

Mounting an LEDor a miniature projectoron a contact lensproduces a fixedretinal image.

Sensory adaptation handouts

The physics of lightThe physics of light

Light energy characteristicsLight energy characteristics– Waves and particlesWaves and particles– Frequency:Frequency:

» The visible spectrum: 380nm to 760 nmThe visible spectrum: 380nm to 760 nm

•Ultraviolet and infrared•Amplitude or intensity•Purity

The structure of the eye and the The structure of the eye and the physics of lightphysics of light

Physics of light and the visual Physics of light and the visual systemsystem

•Sensitivity and reliability• Retinal cells• Rods and cones• The fovea• The blind spot•Accommodation•Binocular disparity

Color visionColor vision

Young & Helmholtz’s Young & Helmholtz’s trichromatictrichromatic theory: theory: Different colors are sensed by cones containing Different colors are sensed by cones containing different photopigmentsdifferent photopigments– Green photopigment, in 50% of cellsGreen photopigment, in 50% of cells

– Red photopigment, in 45% of cellRed photopigment, in 45% of cell

– Blue photopigment, in 5% of cellsBlue photopigment, in 5% of cells Sensed color depends on which combinations of Sensed color depends on which combinations of

cones are absorbing light in their cones are absorbing light in their photopigments.photopigments.

Opponent process theoryOpponent process theory

Hering’s theory of ganglion cellsHering’s theory of ganglion cells– Red/Green cellsRed/Green cells– Yellow/ Blue cellsYellow/ Blue cells– Sensed color is coded by rate of firing: Faster Sensed color is coded by rate of firing: Faster

for red and yellow; slower for green and blue.for red and yellow; slower for green and blue. Habituation of ganglion cells produces Habituation of ganglion cells produces

negative afterimages.negative afterimages.

Negative afterimagesNegative afterimages

Color BlindnessColor Blindness

Sex-linked conditions: Genes on X Sex-linked conditions: Genes on X chromosome, so more common in men.chromosome, so more common in men.– Protanopia, missing red photopigmentProtanopia, missing red photopigment– Deuteranopia, missing green photopigmentDeuteranopia, missing green photopigment

Non-sex-linked conditionNon-sex-linked condition– Tritanopia, missing blue photopigment or blue Tritanopia, missing blue photopigment or blue

conescones

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What do you see?

What do you see?What do you see?