Sensation and Perception - Norwell High School...Sensation and perception chapter 6 Thursday,...

Sensation and Perception

chapter 6

Thursday, January 16, 14

OverviewOur sensational senses

VisionHearing

Other sensesPerceptual powers

Puzzles of perception

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DefinitionsSensationThe detection of physical energy emitted or reflected by physical objects

Occurs when energy in the external environment or the body stimulates receptors in the sense organs

PerceptionThe process by which the brain organizes and interprets sensory information

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Ambiguous figure

Colored surface can be either the outside front surface or the inside back surface.But not simultaneously both

The brain can interpret the ambiguous cues in two different ways.

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Riddle of separate sensations

Sense receptorsSpecialized cells that convert physical energy into electrical energy that can be transmitted as nerve impulses to the brain

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Sensation and perception

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Specific nerve energies

Different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain.

SynesthesiaA condition in which stimulation of one sense also evokes another

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Absolute threshold

The smallest quantity of physical energy that can be reliably detected by an observer

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Absolute thresholds

VisionA single candle flame from 30 miles on a clear night

HearingThe tick of a watch from 20 feet in total quiet

SmellOne drop of perfume in a 6-room apartment

TouchThe wing of a bee on the cheek, dropped from 1 cm

TasteOne teaspoon of sugar in 2 gallons of water

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Difference threshold

The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared

Also called the Just Noticeable Difference (JND)

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Signal-detection theory

A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process

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Sensory adaptation and deprivation

AdaptationThe reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitiousPrevents us from having to respond continuously to unimportant information

DeprivationThe absence of normal levels of sensory stimulation

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Sensory overload

Over-stimulation of the senses

Can use selective attention to reduce sensory overload

Selective attention: the focusing of attention on selected aspects of the environment and the blocking out of others

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Vision

What we seeAn eye on the worldWhy the visual system is not a cameraHow we see colorsConstructing the visual world

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What we see

HueVisual experience specified by color names and related to the wavelength of light

BrightnessVisual experience related to the amount of light emitted from or reflected by an object

SaturationVisual experience related to the complexity of light waves

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What we see

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An eye on the worldCorneaProtects eye and bends light toward lens

LensFocuses on objects by changing shape

IrisControls amount of light that gets into eye

PupilAperture through which light reaches the retina

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An eye on the world

RetinaNeural tissue lining the back of the eyeball’s interior containing the receptors for vision

RodsVisual receptors that respond to dim light

ConesVisual receptors involved in color vision

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Structures of the retina

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Your turnYou have a hard time locating your red car at night, in the poorly lit mall parking lot. Why?1. Your rods are less sensitive to color in dim light.2. Your cones, which detect color, do not function well in dim light.3. Your ganglion cells receive insufficient overall stimulation to function.4. Your rods, which detect color, do not function well in dim light.

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The visual system is not a camera

Much visual processing is done in the brainSome cortical cells respond to lines in specific orientations (e.g., horizontal).

Other cortical cells respond to other shapes (e.g., bulls-eyes, spirals, faces).

Feature detectorsCells in the visual cortex that are sensitive to specific features of the environment

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Huble and Wiesel’s experiment

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Trichromatic theoryYoung (1802) and von Helmholtz (1852) both proposed that the eye detects 3 primary colorsRed, blue, and green

All other colors derived by combination

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Opponent-process theory

A competing theory of color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic

Opponent-process cells are inhibited by a color, and have a burst of activity when it is removed.

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Form perceptionGestalt principles describe the brain’s organization of sensory building blocks into meaningful units and patterns.

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Gestalt principles

ProximityThings close to one another are grouped together

ClosureThe brain tends to fill in gaps to perceive complete forms

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Gestalt principlesSimilarityThings that are alike are perceived together

ContinuitySeeing continuity in lines that could be interpreted as either continuous or abruptly shifting in direction.

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Your turnWhich Gestalt principle is illustrated by the fact that we see columns of dots rather than rows in this diagram?1. Similarity2. Proximity3. Closure4. Continuity

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Depth and distance perception

Binocular cues: visual cues that require the use of both eyes

ConvergenceTurning inward of the eyes, which occurs when they focus on a nearby object

Retinal disparityThe slight difference in lateral separation between two objects as seen by the right and left eyes

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Depth and distance perception

Monocular cues: visual cues that can be used by one eye

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Visual constancies

The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produceShape constancy

Location constancySize constancy

Brightness constancy

Color constancy

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The Müller-Lyer illusion

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Fooling the eyeThe cats in (a) are the same size.The diagonal lines in (b) are parallel.You can create a “floating fingertip frankfurter” by holding hands as shown, 5–10 inches in front of face.

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What we hear

LoudnessThe dimension of auditory experience related to the intensity of a pressure wave

PitchThe dimension of auditory experience related to the frequency of a pressure wave

TimbreThe dimension of auditory experience related to the complexity of a pressure wave

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An ear on the world

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Auditory localizationSounds from different directions are not identical as they arrive at left and right ears.Loudness

Timing

Phase

The brain calculates a sound’s location by using these differences.

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Other senses

Taste: savory sensationsSmell: the sense of scentsSenses of the skinThe mystery of painThe environment within

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Taste: savory sensations

Taste budsNests of taste-receptor cells

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Five tastes

Five basic tastesSalty, sour, bitter, sweet, umami

Different people have different tastes based on:GeneticsCultureLearningFood attractiveness

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Smell: the sense of scents

Airborne chemical molecules enter the nose and circulate through the nasal cavity.Vapors can also enter through the mouth and pass into nasal cavity.

Receptors on the roof of the nasal cavity detect these molecules.

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Sensitivity to touch

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Gate-control theory of pain

Experience of pain depends in part on whether the pain gets past a neurological “gate” in the spinal cord.

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Gate-control theory revised

The matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.

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The environment within

KinesthesisThe sense of body position and movement of body parts

EquilibriumThe sense of balance

Semicircular canalsSense organs in the inner ear, which contribute to equilibrium by responding to rotation of the head

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The visual cliff

Glass surface, with checkerboard underneath at different heightsVisual illusion of a cliffBaby can’t fall

Mom stands across the gap.

Babies show increased attention over deep side at age 2 months, but aren’t afraid until about the age they can crawl.

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Critical period

If infants miss out on experiences during a crucial period of time, perception will be impaired.

When adults who have been blind since birth have vision restored, they may not see well.

Other senses such as hearing may be influenced similarly.

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Psychological and cultural influences

We are more likely to perceive something when we need it.

What we believe can affect what we perceive.

Emotions, such as fear, can influence perceptions of sensory information.

Expectations based on previous experiences can influence perception.Perceptual set: a habitual way of perceiving, based on expectations

All are influenced by culture.

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Perception vs. persuasion

Although subliminal priming can influence judgments and preferences, research doesn’t support its success in major levels of persuasion.

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Extrasensory perception

The ability to perceive something without ordinary sensory information

Has not been scientifically demonstrated

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