Dr. Donna Ayala October 21, 2008

Psychology 1

Chapter 3: Sensation and Perception

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What is sensation? Sensation refers to the detection and basic

sensory experience of environmental stimuli - ex: such as sounds, objects, and odors

All sensation is a result of the stimulation of specialized cells, called sensory receptors , by some form of energy

Transduction: physical energy that is coded into neural signal that can be processed by the nervous system

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Sensory Thresholds

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Senses are specialized into two ways The absolute threshold is the point where

something becomes noticeable to our senses.  It is the softest sound we can hear or the slightest touch we can feel.  Anything less than this goes unnoticed.  The absolute threshold is therefore the point at which a stimuli goes from undetectable to detectable to our senses.

Difference threshold:.  The difference threshold is the amount of change needed for us to recognize that a change has occurred.  This change is referred to as the Just Noticeable Difference

Sensory Threshold

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Imagine holding a five pound weight and one pound was added.  Most of us would notice this difference.  But what if we were holding a fifty pound weight?  Would we notice if another pound were added?  The reason many of us would not is because the change required to detect a difference has to represent a percentage.  In the first scenario, one pound would increase the weight by 20%, in the second, that same weight would add only an additional 2%.  This theory, named after its original observer, is referred to as Weber's Law.

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Absolute Thresholds for Humans

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

SIGHT/VISION

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A) the visual system works on sensing and perceiving light waves. Light waves vary in their length and amplitude:

a) wave length (also referred to as frequency, since the longer a wave, the less often/quickly it occurs) - affects color perception (ex., red=approx 700, yellow approx 600)

b) wave amplitude (this is the size/height of the wave) - affects brightness perception.

Structure of The EYE:

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1) Cornea - the round, transparent area that allows light to pass into the eye.

2) Lens - the transparent structure that focuses light onto the retina.

3) Retina - inner membrane of the eye that receives information about light using rods and cones. The functioning of the retina is similar to the spinal cord - both act as a highway for information to travel on.

4) Pupil - opening at the center of the iris which controls the amount of light entering the eye. Dilates and Constricts.

Rods and Cones

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Rods & Cones - many more rods (approximately 120 million) than cones (approx 6.4 million).

a) cones - visual receptor cells that are important in daylight vision and color vision.

the cones work well in daylight, but not in dim lighting. This is why it is more difficult to see colors in low light.

most are located in the center of the retina...called the FOVEA, which is a tiny spot in the center of the retina that contains ONLY cones...visual acuity is best here.

SO...when you need to focus on something you attempt to bring the image into the fovea.

b) rods - visual receptor cells that are important for night vision and peripheral vision.

the rods are better for night vision because they are much more sensitive than cones.

in addition, the rods are better for peripheral vision because there are many more on the periphery of the retina. The cones are mostly in and around the fovea but decrease as you go out.

to see best at night, look just above or below the object...this keeps the image on the rods.

Color Vision

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Seeing In Color - we can see many colors, but only have 3 types of cones that receive information about color. We have cones that pick up light waves for red, green, and blue.

Color Vision Theories:1) Trichromatic Theory - this theory indicates that we

can receive 3 types of colors (red, green, and blue) and that the cones vary the ratio of neural activity (Like a projection T.V.). The ratio of each each color to the other then determines the exact color that we see.

2) Opponent-Process Theory - color perception depends on the reception of pairs of antagonist colors. Each receptor can only work with one color at a time so the opponent color in the pair is blocked out. Pairs = red-green, blue-yellow, black- white (light-dark).

Color Vision

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DOES COLOR EXIST? People just assume that because we see colors, that they actually exist in the world. In other words, that when they see the color red, that red is a real, physical, tangible, "thing". But is it, or is color just a matter of our perception? If we had different types of nervous systems, we would see things differently (literally) and so wouldn't we think those other things we saw were the real "things"? Let's examine this question of perception a bit further.

What is perception?

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Perception occurs when we integrate, organize, and interpret sensory information in way that is meaningful

Perceptual Organization- Gestalt

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Visual Capturetendency for vision to dominate the other senses

Groupingthe perceptual tendency to organize stimuli into coherent groups

Perceptual Organization- Gestalt

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Gestalt- an organized wholetendency to integrate pieces of information

into meaningful wholesGrouping Principles

proximity- group nearby figures togethersimilarity- group figures that are similarcontinuity- perceive continuous patternsclosure- fill in gapsconnectedness- spots, lines and areas are

seen as unit when connected

Illusions

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Illusions - an incorrect perception caused by a distortion of visual sensations.

1) Muller-Luyer Illusion2) Reversible Figures - ambiguous sensory

information that creates more than 1 good form. For example, the picture of two faces looking toward each other that is also a vase. I am sure most every Introductory Psychology book has this example.

3) Impossible Figures - objects that can be represented in 2-dimensional pictures but can not exist in 3-dimensional space despite our perceptions. You know the artist, Escher who draws the pictures like...the hands drawing each other, the waterfall that goes down and stays level at the same time, etc...

Perceptual Organization- Grouping Principles

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Perceptual Organization-Depth Perception

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Depth Perceptionability to see objects in three dimensionsallows us to judge distance

Binocular cuesretinal disparity

images from the two eyes differ closer the object, the larger the disparity

convergenceneuromuscular cuetwo eyes move inward for near objects

Perceptual Organization-Depth Perception

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Perceptual Organization-Depth Perception

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Monocular Cues (cont.)relative height

higher objects seen as more distantrelative motion

closer objects seem to move fasterlinear perspective

parallel lines converge with distancerelative brightness

closer objects appear brighter

Perceptual Interpretation

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Perceptual Adaptation(vision) ability to adjust to an artificially displaced visual fieldprism glasses

Perceptual Seta mental predisposition to perceive one thing and not another

Group Activity

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See individual task