Sensation and Perception Chapter Three Sensation and Perception Copyright © Houghton Mifflin Company. All rights reserved.

Sensation What is sensation? The process that detects stimuli from the from the external world and converts them onto neural impulses. Sensory receptors- specialized cells that detect stimuli Eyes Ears Nose Mouth Joints, muscles Skin Copyright © Houghton Mifflin Company. All rights reserved.

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“Here’s Lookin at you kid” Perception- The process that organizes sensations into meaningful patterns Not mechanical at all, unlike a neural impulse Meaningful patterns are inner representations of the world Schemas- Different experiences and expectations and ways we organize information about the world. Copyright © Houghton Mifflin Company. All rights reserved.

How do we study sensation and perception? A change in environment triggers chemical and electrical activity in receptors. Sequential processing in the nervous system forms a pattern of activity in a certain area of the brain.(Sensation) Brain assembles bits and pieces of sensory information into meaningful impressions of the world (Perception)Psychophysics- Psychophysics-the study of the relationship between sensation and perception. Copyright © Houghton Mifflin Company. All rights reserved.

Absolute Thresholds for Humans Reading: Ernst Weber – Classic Experiments in Psychology SENSE STIMULUS RECEPTORS THRESHOLD Vision Electromagnetic Energy Rods & Cones in the retina A candle flame viewed from a distance of about 30 miles on a dark night Hearing Sound Waves Hair cells of the inner ear The ticking of a watch from about 20 feet away in a quiet room Smell Chemical substances in the air Receptor cells in the nose About one drop of perfume diffused throughout a small house Taste Chemical substances in saliva Taste buds on the tongue About 1 teaspoon of sugar dissolved in 2 gallons of water Touch Pressure on the skin Nerve endings in the skin The wing of a fly falling on a cheek from a distance of about 0.4 inches

Absolute and Difference Thresholds How much sugar is needed for you to taste it in 2 gallons of water? The odor of a perfume in a room? How loud does your name have to be called out for you to hear it? Absolute threshold- the minimum amount of stimulation an individual can detect through a given sense. Copyright © Houghton Mifflin Company. All rights reserved.

Subliminal Perception Stimuli presented below level of conscious awareness Subliminal perception- the unconscious perception of stimuli that are to weak to exceed the absolute threshold for detection Can it influence attitudes or behavior? Copyright © Houghton Mifflin Company. All rights reserved.

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How soon can you detect changes in light or temperature? Difference threshold, just-noticeable difference (jnd)-minimal differences between two stimuli that people can reliably detect. Weber’s law- minimum change in stimulation that can be detected 50% of the time by a given person Weight 1/50th Light 1/60th Copyright © Houghton Mifflin Company. All rights reserved.

TYPE OF DISCRIMINATION WEBER’S CONSTANT (WEBER’S FRACTION) WEBER's Constant/Fraction SENSE TYPE OF DISCRIMINATION WEBER’S CONSTANT (WEBER’S FRACTION) VISION Brightness of light 1/60 HEARING Pitch (frequency) of a tone 1/333 Loudness of a tone 1/10 TASTE Difference in saltiness 1/5 SMELL Amount of rubber smell TOUCH Pressure on the skin surface 1/7 Deep pressure 1/77 Difference in lifted weights 1/53

Sensitized vs. Desensitized Sensory adaptation-sensory receptors respond less and less to an unchanging stimulus Lets us detect important changes in the env while ignoring unchanging ones You will not adapt to extreme sensations because to ignore these could be harmful Copyright © Houghton Mifflin Company. All rights reserved.

Responder Bias How ready are you to report the presence of a stimulus? Biology vs. nurturing Some individuals’ N . S. are more in tune with certain senses While some learn to use these more like Helen Keller Copyright © Houghton Mifflin Company. All rights reserved.

Seeing the Light Light Physical energy, electromagnetic radiation Wavelength corresponds to color 350-750 nanometers Copyright © Houghton Mifflin Company. All rights reserved.

Electromagnetic spectrum visible to humans Copyright © Houghton Mifflin Company. All rights reserved.

Parts of the Eye (Figure 3.3) Copyright © Houghton Mifflin Company. All rights reserved.

The Eye Cornea- clear covering on the eye surface Iris-a muscle that contracts or expands to regulate the amount of light that enters the eye. (Reflex action) Pupil-black opening inside the iris, size adjusts to the amount of light Lens: accommodation-process by which the lens changes its shape to images more clearly Copyright © Houghton Mifflin Company. All rights reserved.

Fovea- area in the retina where images are sharpest in focus Retina: inner surface of the eye that receives the image as light strikes it through its photoreceptors Fovea- area in the retina where images are sharpest in focus Bipolar cells, ganglion cells Copyright © Houghton Mifflin Company. All rights reserved.

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Photoreceptors: convert physical energy of light into neural signals Cones- color vision and detail in bright light Rods detect objects in low light Perception of brightness Copyright © Houghton Mifflin Company. All rights reserved.

Light to Neural Impulses (Figure 3.5)

Where is your blind spot? The part of the retina where the optic nerve leaves the eye Why? Contains no rods or cones Why didn’t you notice before? Eyes constantly move and they work together Copyright © Houghton Mifflin Company. All rights reserved.

Where are the following? Blind spot Iris Pupil Lens Cornea Optic Nerve Retina FIGURE 4.3 In the human eye, light travels through the pupil to the lens and is then reflected onto the retina. The optic nerve sends the visual information to the brain.

How does the brain translate light into visual images? Feature Detectors are neurons that respond to specific features of the visual stimulus such as horizontal and vertical lines, movement, depth, colors, etc Copyright © Houghton Mifflin Company. All rights reserved.

Color Vision Helmholtz: Trichromatic theory 3 types of color receptors: Red, green, blue-violet By these 3 responding we are able to see colors Hering: Opponent-process theory Afterimages 3 Pairs of opposite colors- they transmit color for either one at a time Red-Green Blue-Yellow Black-White Copyright © Houghton Mifflin Company. All rights reserved.

VISUAL PROBLEMS Color Blindness Color Blind – sensitive to only black & white Dichromat – only sensitive to certain colors – partially color blind Trichromat – normal color vision

Color blindness Color blindness is caused by a defect in the retina or in the cones. Partial color blindness, called dichromatism, consists generally of the inability to differentiate between the reds and the greens or to perceive either reds or greens. Copyright © Houghton Mifflin Company. All rights reserved.