sensation and perception

Sensation

The process by which the sense organs gather

information about the environment and transmit

the information to the brain for initial processing

• Involves transduction of external stimuli (visual, auditory, tactile information) into action potentials.

• The initial step where sensory organs transmit information about color, shape, edges, lightness, and darkness to the brain

Perception

The process by which the brain selects, organises and interprets sensations.

• Involves previous experiences, memories, and associations to create a conscious experience.

• Perception uses sensory information and matches it with memories and experiences

Three broad principles

emerge with regard to sensation and perception:

There is no one-to-one correspondence

between physical and psychological reality;

measuring this is the realm of psychophysics.

• Our conscious experience doesn't perfectly match the physical world.

• The relationship isn't random; it's often orderly and predictable.

•  

• The exact correspondence between physical and psychological reality is one finding off Psychophysics: The study of the relationship between physical and psychological reality.

 

2. Sensation and perception are active processes.

• We actively construct and organize experiences, rather than passively receiving information.

• Sensation is Act of translation, converting external energy into internal vision or a presentation

• E.g. would turn our ear towards potentially threatening sounds

• Focus our attention to particular relevant needs no environment

 

3. Sensation and perception are adaptive

(facilitation of survival and reproduction)

• Senses evolved to aid survival and reproduction.

• Example: Innate tendency to perceive faces, crucial for survival.

• Drafted our senses/adaption to serve survival reproduction functions

 

Features common to all sensory systems

1. Each sensory system has sensory receptors that:   Translation of Physical Energy into Sensory Signals: Sensory receptors translate physical energy into sensory signals. Receptors are specific to each sense. They transform physical energy (e.g., light waves, sound waves) into electrochemical signals/action potentials. Transduction: Process of converting physical energy into neural signals. Action potentials are transmitted along axons to the central nervous system for integration.

2. Each sensory system requires a minimum amount of energy to activate the system (threshold).   All senses have threshold below which a person does not sense anything despite external stimulation. Each sensory system requires a minimum amount of energy to be activated (sensory threshold). Below this threshold, nothing is sensed.

3. Sensation requires constant decision making   Even above the sensory threshold, unconscious decisions occur to distinguish meaningful from irrelevant stimulation. Example: A door opening night wake you up at night but not during the day. Example: Fan on a hot night, as loud as door or window, won't wake you.

4. Sensing the world requires the ability to detect changes in stimulation.   Sensing the world requires detecting changes in energy (e.g., heavier/lighter, brighter/dimmer).

5. Efficient sensory processing requires “turning down the volume” or suppressing redundant information Tune out information unnecessary eg sitting on a chair , first feel chair then after time you lend it out Suppression of Redundant Information: The nervous system tunes out unchanging messages. Example: Noticing the hum of an air conditioner or refrigerator initially, but then tuning it out after a few seconds. Sensory adaptation : The tendency of sensory receptors t respond less to stimuli that continue without change Constant sensory input provides no new information about the environment so the nervous system ignores them Also turns down volume on in

Features common to all sensory systems:

 sensory system has sensory receptors that:

 

• Translation of Physical Energy into Sensory Signals:

2. Each sensory system requires a minimum amount of energy to activate the system (threshold).

3. Sensation requires constant decision making- meaningful fro irrelevant

4. Sensing the world requires the ability to detect changes in stimulation.

5. Efficient sensory processing requires “turning down

the volume” or suppressing redundant information

1. Each sensory system has sensory receptors that:

• Translation of Physical Energy into Sensory Signals:

  • Sensory receptors translate physical energy into sensory signals.

  • Receptors are specific to each sense.

  • They transform physical energy (e.g., light waves, sound waves) into electrochemical signals/action potentials.

  • Transduction: Process of converting physical energy into neural signals.

  • Action potentials are transmitted along axons to the central nervous system for integration.

2. Each sensory system requires a minimum amount of energy to activate the system (threshold).

All senses have threshold below which a person does

not sense anything despite external stimulation.

• Each sensory system requires a minimum amount of energy to be activated (sensory threshold).

• Below this threshold, nothing is sensed.

3. Sensation requires constant decision making

• Even above the sensory threshold, unconscious decisions occur to distinguish meaningful from irrelevant stimulation.

• Example: A door opening night wake you up at night but not during the day.

• Example: Fan on a hot night, as loud as door or window, won't wake you.

4. Sensing the world requires the ability to detect changes in stimulation.

• Sensing the world requires detecting changes in energy (e.g., heavier/lighter, brighter/dimmer).

5. Efficient sensory processing requires “turning down

the volume” or suppressing redundant information

Tune out information unnecessary eg sitting on a chair , first feel chair then after time you lend it out

• Suppression of Redundant Information:

  • The nervous system tunes out unchanging messages.

  • Example: Noticing the hum of an air conditioner or refrigerator initially, but then tuning it out after a few seconds.

Sensory adaptation :

• The tendency of sensory receptors t respond less to stimuli that continue without change

• Constant sensory input provides no new information about the environment so the nervous system ignores them

• Also turns down volume on information that would overwhelm the brain

Subliminal perception

• Process that occurs outside of conscious awareness

• Stimulus Passes our absolute threshold but does not cause a difference that we a able to consciously precess it

• Eg: priming images for fraction of a second influences later decisions  

Absolute threshold

• Sensory systems require a minimum amount of energy for activation (absolute threshold).

 

• The absolute threshold is the minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time.

 

Variability of Absolute Thresholds

• Absolute thresholds vary from person to person and situation to situation.

• The biggest reason they vary is the incidence of external noise in the system.

Noise Impact

Irrelevant distracting information

Some noise can be external :Irrelevant information being processed by the system, such as ambient light or the humming of a fan; this makes it difficult to pick up a particular signal.

• Internal Noise: Neurons fire randomly all the time; this random firing can make it difficult to detect a signal because the signal has to be stronger than the random background firing.

• Internal noise Psychological Factors: Expectations, motivation, stress levels, and fatigue can affect /vary thresholds.

Difference Thresholds:

Just Noticeable Difference (JND):

The lowest level of stimulation required to sense that a change

in stimulation has occurred

• Difference in intensity between two stimuli that is necessary to produce JND

 

• Focus shifts to how much difference between stimuli is required to reliably detect a difference rather than the minimum amount of energy that can be detected.

• Depends o intensity of new stimulus and level of stimulation already present

• The larger the existing stimulus the lager the change needs to be

• Unlike the absolute threshold, the difference threshold changes substantially depending on the stimulus intensity

Weber’s Law:

Regardless of the magnitude of two stimuli, the second must differ by a constant proportion from the first to be perceived as different.

Sensory Thresholds

The JND is not a fixed amount

 

Weber Fraction:

The ratio of change in intensity required to

produce a JND, compared to the previous intensity of the stimulus, expressed as a fraction.

 

Object 1 weighs 100 grams. Difference noted at

103 grams.

 JND=3 grams.

 WF = 3/100 = .03

 

Object 2 weighs 1000 grams. Difference noted

at 1030 grams.

 JND = 30 grams.

 WF = 30/1000 = .03.

 

Weber’s Law: the WF is constant!

• The Weber fraction is constant in this case because we are judging weight in both cases.

• The exact Weber fraction varies depending on the sensory stimuli being used and the individual.

• It does not depend on the starting weight of the object.

Fechner’s Law:

The magnitude of a stimulus grows geometrically(1,2,4,8,16…) as the subjective experience of intensity grows arithmetically.(1,2,3,4,5,)

 

• Gustave Fechner extended Weber's law to estimate the psychological experience of a stimulus.

• Argued that the subjective intensity of sensation is based on the amount of stimulus energy present.

• Found a logarithmic relationship between physical stimulus and subjective intensity; In other words, in order for subjective intensity to increase arithmetically, physical intensity must increase geometrically.

• At low levels of stimulation, a small increase in stimulation is needed to produce an increase in subjective experience.

• At high levels of stimulation, a large increase in physical stimulation is needed to produce an increase in subjective experience.

 

Modification and Graphical Representation

• Fechner's law works most of the time, but it was eventually modified by  Stevens because it did not quite apply to all stimuli and all senses.

• Despite the slight modification, these two laws are conceptually very similar to one another.

Graphical Form

• A small stimulus requires only a small increase in intensity to reach a just noticeable difference.

• A strong stimulus requires a very large increase in intensity to achieve one JND.

Steven’s Power Law

As the perceived intensity of a stimulus grows arithmetically, the actual magnitude of the stimulus grows exponentially (squared, cubed, etc.)1

Signal detection theory

• Signal detection theory helps understand how we make decisions when there are two possible choices.

2 processes are at work for detecting a stimulus :

• Initial sensory process - reflecting observer sensitivity to stimulus/ how well you hear etc

• Decision process - individuals readiness to report detecting a stimulus when uncertain 

4 possible outcomes

Hit

Reporting an actual stimulus or declare correct negative

• Correctly identifying something you should say yes to.

• Miss

  • Fail to report actual; stimulus

Correct Rejection

Properly said no to something you should say no to

False Alarm

• Reporting a stimulus when no one was present

• Something that shouldn't go through gets put through anyway.

Extended Periods of Signal Detection

• Signal detection can become more challenging over extended periods.

• Fatigue can interfere with making yes/no decisions.

• It taxes the attentional system, making it more difficult.

 

Transduction

• Sensation requires converting energy in the world into neural signals.

•  Specialised cells known as sensory receptors transform energy into neural impulses that can be interpreted by the brain. Brain reads neural code- patterns of neural fire ring and translates it into meaningful language

• Sensation starts with converting external energy into internal signals.

• External energy (light, sound) transforms into electrochemical signals called action potentials.

• From sensation to perception to cognition

 

Code for intensity and quality of stimulus;

• Intensity= number of sensory neurons that fire, the frequency or combination it both

• Quality= eg  colour, temperature, pitch= both specific type of receptors involved  and pattern of neural impulses generated 

 

Transduction: the process of converting physical energy or stimulus information into neural impulses.

 

• Sensory receptors facilitate transduction.

• After transduction, the brain interprets neural firing patterns into sensory experiences.

Light as a Stimulus

• In vision, the stimulus is light, a form of electromagnetic radiation or energy that moves in waves.

• Perception of light depends on:

  • Wavelength: Distance from one peak to another, determining color experience.

  • Amplitude: Height of the wave, determining brightness experience.

 

The Stimulus: Light

- light= A form of electromagnetic energy that moves in waves

The Visible Spectrum

• The human eye perceives a narrow band of wavelengths.

• Visible Spectrum: Wavelengths between approximately 400 and 750 nanometers, which we can register and transduce.

• The electromagnetic spectrum ranges from short wavelengths

gamma rays to long wavelength radio waves.

Limitations of Sensory Perception

• Limitations of senses restrict what we can perceive and experience.

 

Example: Vision of Bees

• Bees see wavelengths down to about 307 nm (ultraviolet light).

• Bees perceive colors and patterns not visible to humans, helping them locate pollen and nectar in flowers.

 

Implications of Sensory Limitations

• Sensory receptors transduce information, and their limitations define our conscious experience of the world.

 

Light Entry and Focusing

1. Light enters the eye through cornea, a transparent tissu covering the front of the eyeball

2. From cornea light passes through a chamber of fluid= aqueous humour A fist at in alphabet is first in the eye, which supplies oxygen ad other nutrients to the cornea and lense 

3. Light travels though the pupil an opening centre of the iris (pigmented tissue for eye colour ),

4. Lense( disc-shaped structure )invoked in focusing the eye

5. Light is the projected through vitreous humour (clear, gelatinous fluid) onto retina (a light sensitive layer of tissue at the back if the eye), it transduces light into visual sensations ? Neural impulses / Psychological meaningful information 

Pupillary Response

• Iris muscles control the pupil's size.

  • The pupil expands (dilates) or contracts to regulate light entry.

  • Pupils dilate in the dark to allow more light in.

  • Pupils constrict in bright light to protect the eye from excessive light.

  • Pupillary response: Dilation and constriction of pupils based on light levels.

  • Constriction is faster than dilation.

    • This protects retinal receptors from sudden bright light.

Emotional and Motivational Influence on Pupil Size

• Pupil size also changes with emotions, motivation, and other factors.

• Dilated pupils can indicate arousal or readiness.

• Psychology researchers use pupillary response to study:

 

• Emotions

• Motivation

• Sexual attraction

• Concentration

 

Retinal Structure

• The retina is thin (about the thickness of a sheet of paper).

• It consists of multiple layers of cells.

• The innermost layer contains photoreceptors.

  • Photoreceptors: Sensory receptors that transduce light energy into neural signals.(rods and cones )

 

Photoreceptors

• Two types of photoreceptors:

  • Rods: Rod-shaped photoreceptors.

  • Cones: Cone-shaped photoreceptors (pointed at the top).

 

Rods are more sensitive to light than cones.

• Rods enable vision in low light conditions.

• Rods do not allow color perception, resulting in black and white vision in low light.

 

Cones are less sensitive than rods.

• Cones require stronger light conditions to respond.

• Cones are sensitive to different wavelengths of light, enabling color vision.

• Cones facilitate sharper vision by responding selectively to light from specific locations.

Retinal Layers and Neural Pathways

1. When rod or con absorb light energy, it generates an electrical signal, stimulating the neighbouring Bipolar cells

2. Bipolar cells combine information form many receptors and produce grated potentials on ganglio cells , which integrate information from multiple bipolar cells.

3. The long axons of these ganglion cells bundles together form the optic nerve, which carries visual information to the brain

 

The central region of the retina, the fovea is the most sensitive for small detail, so vision is the sharpest

In contrast point of the retina where optic nerve leave the eye= blind spot has no receptor cells   

Distribution of Rods and Cones across the Retina

• Cones are mostly concentrated in the fovea (center of the retina).

  • The fovea is used for detailed visual processing, such as reading.

  • The fovea enables color vision.

 

Rods are more distributed in the periphery of vision.

• Peripheral vision is less clear than central vision.

The Fovea

• The fovea is a central region of the retina densely packed with cones.

• It provides the clearest area of vision.

• The fovea enables rich color representation.

• It is used for reading.

• The fovea is small, measuring about 1 -2 degrees of visual angle in size.

• Eye movements are made to bring important information into the fovea for clearer perception.

Cornea

transparent tissu covering the front of the eyeball

Aqueous Humor

 a chamber of fluid= aqueous humour A fist at in alphabet is first in the eye, which supplies oxygen ad other nutrients to the cornea and lense 

iris

pigmented tissue for eye colour

Pupil

opening centre of the iris

vitreous humour

clear, gelatinous fluid

retina

1. light sensitive layer of tissue at the back if the eye), it transduces light into visual sensations ? Neural impulses / Psychological meaningful information 

Colour 3 psychological dimension

: hue, saturation and lightness 

 

Hue is what people commonly mean by colour — that is, whether an object appears blue, red, violet and so on.

 

Saturation is a colour's purity (the extent to which it is diluted with white or black, or "saturated' with its own wavelength, like a sponge in water).

 

 Lightness is the extent to which a colour is light or dark.

Trichromatic Theory

• Hypothesized three receptor types in the eye, each maximally sensitive to particular wavelengths (blue, green, red).

• Input from these cones is integrated to perceive all other colors.

• Similar to mixing paints or light to create new colors.

• The theory accurately predicted the existence of three cone types,

• Each cone responds to arrange waves but most persistently waves of light in a particular point of the spectrum

• Short wavelength cones (s-cones)= more sensitive to wavelength of about 420 MM / perceived as blue

• Middle wavelength  cones (M-cones)= sensation of green, Sensitive to wave lengths of about 535nm

• Long wavelength cones (L-cones) wave lengths about 560 nm/produces red sensation

 

Color Blindness

• The trichromatic theory accounts for color perception deficits in individuals missing one or more cone types (color blindness).

Limitations of Trichromatic Theory:

Afterimages

• Trichromatic theory cannot explain certain phenomena like color afterimages.

• Experiment: Staring at a yellow and red image creates a blue and green afterimage.

• The question of why staring at yellow leads to perceiving blue, and staring at red leads to perceiving green, remains unanswered by trichromatic theory.

Opponent Process Theory

• theory.

• Suggests all colors are derived from three antagonistic color systems:

  • Black and white.

  • Blue and yellow.

  • Red and green.

  • Fatiguing the blue-yellow system by staring at yellow results in perceiving blue when the yellow color is removed.

  • Fatiguing the red-green system by staring at red results in perceiving green when the red color is removed.

  • Successfully explains color afterimages.

  • The sensory system adapts or responses less  to constant stimulate

  • Visual system adaptation begins with bleaching in the retina

Difference in colour theory

• Both trichromatic and opponent process theories are valid but operate at different stages.

• Trichromatic theory applies to the retina, where three cone types exist.

• Opponent process theory applies to later stages of visual processing in the brain's visual centers.

Bottom up

Detect features of sensory data

Analyse specific features and combine component parts into more complex form

Form perception

Bottom up processing refers to a process that begins at the bottom with raw sensory data that fit up to the brain

• Bottom up explanation of visual perception argues at the brain forms perception by combining the response of multiple feature detectors in the primary cortex which themselves integrate input from their own slow and the visual system

Top down

Top down processing and contrast starts at the top with the observers expectations and knowledge

• The brain uses pride knowledge to begin organising an operating sensations as soon as the information starts coming in rather than waiting for perceptions to form based on sequential step-by-step analysis of their isolated features

• Use prior knowledge and experiences to organise and interpret sensations

Select specific features that meet expectations about stimulus

 

Top-down factors are numerous, but include:

• Context

• Schemas: enduring knowledge structures

• Experience or learning

• Motivation

• Your knowledge of the world

• Your expectations

Top-down factors are very powerful and can

dominate perception

Gestalt laws of perceptual organisation

A small number of basic perceptual rules that the brain automatically unconsciously uses to organise sensory and put into meaningful wholes

 

 

Laws of Perceptual Organization

 

 

Gestalt principles exemplify the way the

brain organises perceptual experience to

reflect the regularities of nature.

• They are “rules of thumb” or Heuristics:

• Reflect experience

• Used unconsciously

• Occasionally misleading

• Based on our experience of how the world works.

• Applied unconsciously to help ease and speed up our perception of the world.

• Usually lead to a correct interpretation of the world, but occasionally misleading and can lead to incorrect perceptions.

 

Law of Similarity

• The brain tends to group together similar elements.

• Example:

• In a 6x6 array of red dots, it's hard to discern rows or columns.

  • When some dots are changed to blue, the brain groups the blue dots together and red dots together, and most people perceive columns.

Law of proximity

 

Objects that are closer together

Law of Proximity

• Objects that are in close physical proximity to one another tend to be grouped together.

Law of Good Continuation

Stimuli tend to be organized into continuous lines or patterns rather than being perceived as discontinuous Elements

Because is the simplest interpretation

 

• We see a continuous rope (round and around) rather than discontinuous elements.

• This is because it is the simplest interpretation.

Law of Closure

Every stimulus pattern completed such that any

gaps are seen as a closed, complete, whole figure.

 

Law of Closure

• Wherever possible, people tend to perceive incomplete figures as complete.

• If part of a familiar shape or pattern is missing, our brains will fill in the missing part to complete the pattern.

• Example: Kanizsa triangle.

  • Most people perceive two triangles (one white and one brown), even though there is no physically present white triangle.

  • The illusory triangle exists due to the law of closure.

 

Law of Familiarity

Things are more likely to form groups if the

groups appear familiar or meaningful

 

Law of Familiarity

• Things are more likely to be grouped if the groups appear familiar or meaningful.

Law of common fate

Law of Common Fate

• Things that move together appear to be grouped together.

Depth perception

Second aspect of perceptual organization is Depth or Distance Perception

• Refers to the organization of perception in three dimensions.

• Our mental representation of the world has three-dimensional properties, despite the information projected onto our retina being two-dimensional.

• We use various cues in a visual scene to establish our sense of depth.

Types of Depth Cues

• Binocular Cues: visual input from two eyes)

• Monocular Cues: (Visual input from one eye)

• Depth perception requires vision.

Binocular Depth Cues

Visual input from both eyes

Convergence

• When looking at a close-up object, our eyes angle inwards towards one another.

• The extra effort made by the muscles on the outside of each eye gives a clue to the brain about how far away the object is.

• Example:

  • Object at 10 cm: Muscles work hard.

  • Object at 1 meter: Muscles work less hard.

  • Object at 4 meters: Muscles don't have to do much work.

  • The brain extrapolates distance by comparing how much work eye muscles do.

Retinal Disparity

 

Because the eyes are slightly different location or but the most distant object produced different image on each retina or retinal disparity

• Slightly different optical images are produced on the retinas of your two eyes when viewing an object.

• By processing information about the degree of disparity between the images from the two eyes, the brain produces the impression of a single object with depth.

• Experiment:

  • Hold up a finger on each hand, one close and one at arm's length.

  • Line up the fingers.

  • Close each eye alternately.

  • Fingers appear to be in slightly different positions in each view.

  • Confirms that two eyes are getting slightly different retinal images, aiding depth perception.

Retinal Disparity

Because the eyes are slightly different location or but the most distant object produced different image on each retina or retinal disparity

• Slightly different optical images are produced on the retinas of your two eyes when viewing an object.

• By processing information about the degree of disparity between the images from the two eyes, the brain produces the impression of a single object with depth.

• Experiment:

  • Hold up a finger on each hand, one close and one at arm's length.

  • Line up the fingers.

  • Close each eye alternately.

  • Fingers appear to be in slightly different positions in each view.

  • Confirms that two eyes are getting slightly different retinal images, aiding depth perception.

 

Convergence

• When looking at a close-up object, our eyes angle inwards towards one another.

• The extra effort made by the muscles on the outside of each eye gives a clue to the brain about how far away the object is.

• Example:

  • Object at 10 cm: Muscles work hard.

  • Object at 1 meter: Muscles work less hard.

  • Object at 4 meters: Muscles don't have to do much work.

  • The brain extrapolates distance by comparing how much work eye muscles do.

Monocular depth perception cues

Visual input from one eye

 

•  Interposition (occlusion): one object blocks another

•  Linear perspective: lines converge

•  Texture gradient: Distant objects appear finer

•  Shading: 3D objects cast shadows

• Arial perspective: Far objects are fuzzy and appear blue-tinted

•  Familiar size: Familiar objects that appear small are inferred to be distant

• Relative size: The smaller of 2 objects is seen as further Away

Interposition or Occlusion

• If one object blocks our view of another, the object doing the blocking must be closer to us.

• Example: Woman holding an umbrella blocking the view of a taxi, she is closer to us than the Taxi.

Linear Perspective

• We perceive depth when we see two parallel lines that seem to converge together in an image.

• Examples:

  • Railway tracks meeting at the horizon.

  • Field of planted crops.

  • Buildings, hallways, or covered arcades

 

 

Texture Gradient

• When looking at textured surfaces, the texture appears coarser at close range and finer and more densely packed at greater distances.

• Examples:

  • Rocky beach: Individual pebbles visible up close, not in the distance.

  • Sahara Desert: Wind patterns visible up close, less clear in the distance.

  • Crowd of people: Individual people distinguishable up close, just a crowd in the distance.

 

 

 

Aerial Perspective

• Also known as atmospheric perspective.

• Light scatters as it passes through space, especially moist, polluted, or dusty air.

• Objects further away appear fuzzier and less clear than those nearby.

• Dust and vapor particles in the atmosphere cause light to bend, making distant objects (like mountains) appear to have a bluish hue.

Familiar Size

iliar Size

• People tend to assume that an object is its usual size.

• Familiar objects that appear smaller than they should are perceived as being distant.

• Example: Cars on a bridge in a historic photograph. The cars mid-span appear much smaller, indicating they are further away.

 

Relatives size

• When looking at two objects that you know to be the same size or very similar sizes to one another, people typically perceive the smaller object as being further away.

• Example: Arc of identical orange balls angling backward, smaller balls perceived as further away.

Shading

3D objects cast shading

Perceptual Constancy

• Perceptual constancy refers to perceiving objects as stable and unchanging despite changes in sensory receptor stimulation.

• Example: Seeing a friend walk away without perceiving them as shrinking, even though their retinal image decreases in size.

• Color Constancy

• Size Constancy

• Shape Constancy

Color constancy:

Tendency to perceive object colour as stable, even under conditions of changing illumination

 

Color Constancy

• Definition: Perceiving object color as stable even under changing illumination.

• Example: Grapes appearing green and an orange appearing orange under different lighting conditions, even when they are the same color.

• Explanation: Our brains account for the lighting conditions to perceive the correct color.

• We are not necessarily consciously aware of how lighting changes colors, but we know that under yellow light a specific muddy color can only have originated from a green object.

• Similarly, under blue light, the same muddy color can only have come from and orange object.

 

Shape constancy:

We recognise an object as having the same shape although we may view it from a different angle, at a different distance

 

Maintain constant perception of the shape of object was spiral the fact that the same typically produces a new different impression on the retina

 

Shape Constancy

• Definition: Recognizing an object as having the same shape even when viewed from different angles or distances.

• Example: A door maintains its shape as it opens, despite the changing shape reflected on the retina.

• Another Example: A clock continues to look like the same circular clock even when viewed from the side and the shape is now oval.

Size constancy:

Objects do not differ in size when viewed from different distances

Objects do not appear to change in size when review from different distances

The closer the object, the larger the image on retina

Car five made us away. Will cost a retinal image five times large as the same car 15 m away yet people do not wonder how the car 15 m away can possibly carry full size passengers.

The reason; The brain corrects for the size of the retinal image based on cue such as the size of objects in the backkround