Sensation & Perception-session3

7/31/2019 Sensation & Perception-session3

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Sensation and

Perception

Tehzeeb Sakina AmirPSY session 3


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Sensation

Basic five senses: Sight Sound Taste Smell Touch

Psychologists believe humans have capabilitiesbeyond these senses and they all are

interrelated for e.g. Touch relates to pain,temperature, vibration etc.Psychologists study SENSATION in relation toPERCEPTION


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Some important terms

Stimulus energy that produces a response in a senseorgan. Stimuli vary in Type & Intensity (light stimuli & sound stimuli)

Psychophysics is the study of relationship betweenthe physical aspects of stimuli and our psychologicalexperience of them.Absolute Thresholds is the smallest intensity of astimulus that must be present for it to be detected These are measured under ideal conditions

Normally our sense can not detect them because of NOISE

which is background stimulation that interferes with other stimuli.Difference ThresholdsSensory adaptation


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Absolute Thresholds

Sight a candle flame can be seen from 30miles away on a dark clear night

Hearing the ticking of a watch can be heard 20

feet away under quiet conditionsTaste sugar can be tasted when 1 teaspoon isdissolved in 2 gallons of water

Smell perfume can be detected when one drop

is present in a three-room apartment.Toucha bees wing falling from a distance of 1cm can be felt on the cheek.


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Difference Thresholds

The smallest level of stimulation required tosense that a change in stimulation has occurredIn other words, it is the minimum stimulationrequired to detect the difference between two

stimuli juts noticeable differenceJust noticeable difference depends on the initialintensity of the stimulus - for e.g. moon,telephone ringing in a quiet vs crowded room

Webers Law just noticeable difference is inconstant proportion to the intensity of an initialstimulus for weight he states it is 1:50


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Sensory Adaptation

An adjustment in sensory capacityfollowing prolonged exposure to stimuli.

People living near airports

Odor in a room

Reason being sensory receptors are moreresponsive to changes in stimulation, constant

stimulation does not produce a reaction.


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Sensory &

perceptualprocesses

Sensation

Perception

Stimulus reception by sensory receptors

Receptors translate it into nerve impulse

Features detectors analyze stimulus features

Stimulus features are reconstructed intoneural representation

Neural representations are compared with

previously stored information in brain

Matching process results in recognition andinterpretation of stimuli


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Perception

Organizing and making sense of what weexperience as stimuli.

Perception is a constructive process bywhich we go beyond the stimuli that arepresented to us and attempt to constructmeaning out of it


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Perception figure & ground


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Perception figure & ground

Reason each figure is 2D

Figure = the object being perceived

Ground = the background or spaces within the

object

Important we do not just passively respond tovisual stimuli that fall on our retina, we actively

try to organize and make sense of what we see.Hence perception is a constructiveprocess


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Perception gestalt laws

Gestalt meansperceptual whole,which is something

greater than the sumof the individualelements.


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Basic principles that describe how weorganize bits & pieces of information intomeaningful wholes. They are valid for

visual stimuli Closure

Proximity

Similarity

Simplicity

Continuity


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Simplicity


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Perception similarity


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Perception proximity,connectedness and continuation


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Perception feature analysis

A theory of perception according to which weperceive a shape, pattern, object or scene byreacting first to the individual elements that

make it up.

R

Stimulus SensationFeature

detectionHigh levelanalysis

Integration Perception


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Feature Analysis Treismanperspective

Perception of objects is a two-stageprocess:

Pre-attentive stage we pay attention to the

physical features of a stimulus like size, color,shape, movement etc

Focused attention stage we focus

particular features of the object, choosing andemphasizing features that were initiallyconsidered separately.


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Perception is Processing

Top-downprocessingis guidedby higher level

knowledge,experience,expectations andmotivations.

Bottom-upprocessingconsistsof recognizing and

processinginformation about theindividualcomponents of the

stimuli

Both processes occur simultaneously and Interact with each other


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Perceptual Constancy

It is a phenomenon in which physical objectsare perceived as unvarying andconsistent, despite changes in their

appearances or in the physicalenvironment.


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Depth perception

The ability to view the world in three dimensionsand to perceive distance.

It is generally because we have two eyes! And the

distance between them cause a slightly differentimage on the retina.

That difference in images is known as Binoculardisparity.

This disparity varies according to the distance ofthe objects.


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Monocular cues

Sense of distance & depth can be obtained with just oneeye is monocular cues

1. Motion Parallax is the change in the position ofan object on the retina due to movement of head, the

brain calculates the distance of the object by theamount of change in the retinal image.

2. Relative Size the object with smaller image isfarther away than the object with larger image,experience has taught us.

3. Linear Perspective distant objects appear to becloser together than nearer ones, it helps in estimationdistance, making 2D image into 3D.


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Motion Perception

Several cues provide us motion perception:

1. Movement of the object image on retinais perceived relative to stablebackground.

2. When stimulus is heading towards us,the image on the retina will expand insize, filling our visual field, we assumestimulus is approaching.


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Perceptual illusions

Errors in perceptions or falseperceptions

Stadiums, buildings, highways etc

Devils tuning

fork 3 or 2prongs???


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Perceptual illusions

Poggendorf illusion Muller-Lyer illusion

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Sensation & Perception-session3

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