Sensory, Attentional and Perceptual Processes | CBSE Class 11 Psychology Notes

This note covers sensation and sense modalities, sensory thresholds, attention and its types, theories of selective attention, perceptual processing, the role of the perceiver, perceptual organisation, depth cues, perceptual constancies, illusions, and socio-cultural influences on perception.

How do our senses help us know the world?

Our knowledge of the external world and our own body begins with information collected by the senses. A stimulus is something that stimulates a sense organ, such as light, sound or the fragrance of a flower. Sensory receptors are the systems that receive this information.

Sensation is the initial experience of a stimulus registered by a particular sense organ. It involves detecting and encoding physical stimulation. Experiences such as warm, hard, loud and blue are basic sensory experiences. Each specialised system dealing with a particular kind of information is a sense modality.

Which sensory systems gather information?

The five external sense organs and two deep sensory systems register ten varieties of stimuli. They also distinguish qualities within stimulation: a light may be bright or dim, while a sound may be loud or faint. Receiving information is the beginning of knowing, rather than its complete explanation.

Attention selects certain stimuli from others. Perception recognises, interprets and gives meaning to sensory information. Sensation, attention and perception are highly interrelated and are often treated as elements of cognition, the process of knowing the world.

What are the functional limitations of sense organs?

Sense organs function within a limited range of stimulation. Eyes cannot see things that are very dim or very bright. A stimulus must have an appropriate intensity to be noticed. Psychophysics studies the relationship between physical stimuli and the sensations they produce.

How do absolute and difference thresholds differ?

The absolute threshold, also called absolute limen (AL), is the minimum stimulus value needed to activate a sensory system. Because this value varies, it is assessed over several trials. Operationally, it is the value detected on 50 per cent of occasions.

The difference threshold, or difference limen (DL), is the smallest difference between two stimuli needed to notice them as different. It is the minimum change that produces a difference in sensation on 50 per cent of trials.

How can the sugar-water procedure illustrate thresholds?

1. Begin with plain water and add sugar granules one after another.
2. Taste the water as sugar is added and identify when sweetness is first experienced.
3. Remember this sweetness, then continue adding sugar and tasting.
4. Identify when the new sweetness is distinguishable from the previous sweetness; assess detection over repeated trials using the 50 per cent criterion.

The absolute threshold is not fixed. It varies considerably across people and situations with bodily conditions and motivational states. Sensation also depends on receptors, connecting nerve pathways and brain areas. Receptors encode stimulation as electrical impulses that must reach higher brain centres to be noticed.

Structural or functional damage to a receptor, its neural pathway or the relevant brain area may cause partial or complete loss of sensation. Thus, stimulus intensity alone cannot explain whether a person experiences a sensation.

What are the main properties of attention?

Many stimuli reach our senses simultaneously, but we notice only a selected few at a time. Entering a classroom exposes us to chairs, windows, students and schoolbags. Attention selects one or two objects from this larger field rather than registering every object equally.

Attention involves more than selecting an object. It also concerns readiness, focused awareness and the effort devoted to looking for something. In this sense, attention is an allocation of effort.

The focus of attention is the object or event at the centre of awareness. The fringe of attention contains objects or events away from that centre, of which we are only vaguely aware. These describe different positions within awareness.

A process-oriented classification distinguishes selective and sustained attention. Selective attention concerns choosing a limited number of stimuli. Sustained attention concerns maintaining attention over time. Divided attention occurs when attention is allocated to more than one activity at the same time.

Which factors determine selective attention?

The perceptual system has a limited capacity to receive and process information. Selective attention therefore chooses a few stimuli from the many available. Its determinants concern both the features of stimulation and the characteristics of the person attending.

What are the external factors?

External factors are features of the stimuli themselves. Other things held constant, size, intensity and motion appear to be important determinants. Large, bright and moving stimuli easily attract attention. Novel stimuli and those of moderate complexity also readily enter its focus.

Human photographs are more likely to receive attention than photographs of inanimate objects. Rhythmic sounds are more readily attended to than verbal narrations. Sudden and intense stimuli also have a strong capacity to attract attention.

What are the internal factors?

Internal factors lie within the individual. Motivational factors arise from biological or social needs. Hunger makes even a faint food smell noticeable. A student taking an examination is likely to attend to the teacher's instructions more than other students.

Cognitive factors include interest, attitude and preparatory set. Interesting objects attract attention readily, as do objects towards which a person is favourably disposed. A preparatory set is a mental readiness to act in a certain way and respond to one kind of stimulus rather than others.

The distinction is between the stimulus and the person, not between two unrelated processes. Selection can reflect the qualities of what is present as well as the needs, interests and readiness of the observer.

How do theories explain selective attention?

Theories of selective attention explain how some information receives further processing while other information receives less. They differ over whether unselected information is screened out, weakened, or selected at different stages of processing.

What does filter theory propose?

Filter theory, developed by Broadbent in 1956, describes a bottleneck when many stimuli enter receptors simultaneously. A bottleneck is a restriction on how much information can proceed. Stimuli pass through short-term memory, the system temporarily holding information, before reaching a selective filter.

The filter allows only one stimulus through for higher processing at that moment. Other stimuli are screened out. Awareness is therefore limited to the stimulus that gains access through the filter.

How does filter-attenuation theory modify this account?

Filter-attenuation theory, developed by Triesman in 1962, proposes that unselected information is not completely blocked. Attenuation means weakening: the filter reduces the strength of that information, allowing some stimuli to reach higher processing.

Personally relevant information, such as one's name at a collective dinner, can be noticed even at a very low sound level. Such weak stimuli may occasionally produce a response by passing through the filter.

What does multimode theory propose?

Multimode theory, developed by Johnston and Heinz in 1978, treats attention as flexible. Selection can occur at three stages:

• Sensory representation: the sensory form of a stimulus, such as its visual image, is constructed.
• Semantic representation: meaning-related information, such as an object's name, is constructed.
• Consciousness: sensory and semantic representations enter awareness.

More processing requires more mental effort. Early selection, based on the first stage, requires less effort than late selection, based on the third stage. This account therefore links the point of selection to the amount of processing required.

How do sustained attention, divided attention and attention span differ?

Sustained attention, also called vigilance, is the ability to maintain attention on an object or event for a long duration. Air traffic controllers and radar readers must monitor signals whose occurrence is usually unpredictable. Errors in noticing them may be fatal.

What influences vigilance?

When can attention be divided?

Divided attention becomes possible only with highly practised activities because these become almost automatic and require less attention than new or slightly practised activities. Automatic processing occurs without intention, takes place unconsciously and involves very little or no thought. Reading words and tying shoelaces illustrate it.

Span of attention, or perceptual span, is the amount of information grasped from a complex display during a single momentary exposure. A tachistoscope is an instrument used to present such brief displays and determine this span.

Miller reported a span of seven plus or minus two. People can attend to five to seven numbers at a time, extendable to nine or more under exceptional conditions. This concerns the amount grasped briefly, whereas vigilance concerns the duration for which attention is maintained.

Attention Deficit Hyperactivity Disorder (ADHD) is described through difficulty sustaining attention, impulsivity and excessive motor activity. Impulsivity involves acting without reflection. Attention difficulties may persist into adolescence or adulthood if not managed properly; they should not simply be equated with lack of intelligence.

How does perception turn sensation into meaning?

Sensation supplies elementary experience, such as a flash of light or a smell. By itself, this does not identify the source. Perception gives meaning to that sensory material using learning, memory, motivation, emotions and other psychological processes.

People often construct their own interpretation of objects and events. Perception is therefore both interpretation and construction from a person's point of view. It does not consist merely of passively receiving a finished picture of the external world.

Arrows connect a stimulus to sensory receptors, then through attention to the brain, learning, memory and other psychological processes, and finally to perception. CNS in the brain label means central nervous system.

See Fig. 4.1 in your NCERT textbook

How do bottom-up and top-down processing compare?

Recognising a dog from its furry coat, legs, eyes and ears illustrates a parts-to-whole account. Identifying the dog first and then recognising these components illustrates the whole-to-parts account. Studies show that both processes interact to help us understand the world.

How does the perceiver influence what is perceived?

The perceiver actively contributes to meaning. Motivation, expectations, past experience, cultural knowledge, memories, beliefs, values and attitudes affect interpretation. The same sensory material need not be constructed in the same way by every observer.

How do motivation and expectations operate?

Motivation, involving needs and desires, strongly influences perception. In experiments using ambiguous pictures, pictures open to more than one interpretation, hungry people perceived food objects more often than satiated people. Satiated here means not hungry.

Perceptual set refers to expectations about what will be perceived in a situation. There is a strong tendency to see what is expected, even when this does not accurately reflect reality. A knock around a milkman's usual delivery time is likely to be interpreted as the milkman's arrival.

An expectancy activity first displays 12, 13, 14, 15, then replaces the surrounding numbers to produce A, 13, C, D. Most people write B in place of 13 in the second display. The changed context affects interpretation of the unchanged middle form.

What is a cognitive style?

A cognitive style is a consistent way of dealing with the environment. Field-dependent people perceive globally, treating the external world as a whole. Field-independent people perceive analytically, breaking it into smaller units.

In a task requiring a hidden triangle to be located within a complex picture, people who locate it quickly are described as field-independent. Those taking longer are described as field-dependent. Differences in experience and cultural learning also modify what people notice and how finely they distinguish it.

How are visual elements organised into meaningful wholes?

Form perception is the organisation of the visual field into meaningful wholes. We perceive a bicycle as a complete object rather than a collection of wheels, saddle and handle. Gestalt means a regular figure or form.

Gestalt psychologists, including Köhler, Koffka and Wertheimer, held that an organised whole differs from the sum of its parts. A flower pot with flowers and the pot without flowers remain wholes, but their configurations, or arrangements, differ. Pragnanz refers to a good figure towards which perceptual organisation is oriented.

What is figure-ground segregation?

Figure-ground segregation separates what stands out as a figure from its background. A figure has definite form, greater organisation and a clear contour, meaning outline. The background is relatively formless and stays behind it.

The figure appears clearer, limited and relatively nearer; the background appears relatively unclear, unlimited and farther away. Words on a page, a painting on a wall and birds against the sky illustrate this organisation.

A white central area is bordered by two black profiles facing one another. The white area can appear as a vase, or the black areas can appear as two faces.

See Fig. 4.3 in your NCERT textbook

Which principles guide grouping?

Three separated blue angles occupy the corners of a triangle. Gaps remain between them, yet the arrangement is perceived as a triangle through closure.

See Fig. 4.10 in your NCERT textbook

How do monocular cues help us perceive depth?

Space is the visual field or surface in which things exist, move or can be placed. Images on the retina, the eye's image-receiving surface, are flat and two dimensional. Depth perception is viewing the world in three dimensions, including distance.

Cues are sources of information used to perceive depth. Monocular cues work with one eye; binocular cues require both eyes. Artists often use monocular information to suggest depth on a flat surface, hence the description pictorial cues.

What are the important monocular cues?

Motion parallax is a kinetic, or movement-based, monocular cue, so it is not considered a pictorial cue. From a moving bus, nearby objects appear to move against its direction, whereas distant objects appear to move with it.

Photograph: Texture gradient (NCERT Class 11 Figure 4.12). The photograph shows a stone wall receding into the distance. Individual stones are more clearly separated nearby; the visible texture becomes denser farther along the wall.

How do binocular cues contribute to distance perception?

Both eyes provide information for depth perception in three-dimensional space. The main processes considered here are retinal disparity, convergence and accommodation. They concern differences between eye images and changes associated with focusing on objects at different distances.

What is retinal disparity?

Retinal disparity, or binocular disparity, is the difference between the images of the same object on the two retinas. Our eyes are separated horizontally by about 6.5 centimetres, so the two images are slightly different.

The brain interprets a large disparity as indicating a nearby object and a small disparity as indicating a distant one. The difference is therefore greater for near objects and smaller for far objects.

What are convergence and accommodation?

Convergence is the inward turning of the eyes when looking at a nearby object. Eye muscles send information to the brain about the degree of inward turning. Greater convergence makes an object appear nearer; convergence decreases as the object moves farther away.

Accommodation is focusing an image on the retina by changing lens thickness. The ciliary muscle, the muscle producing this change, relaxes when the object is more than 2 metres away. As the object moves nearer, it contracts and the lens becomes thicker.

Signals about the degree of muscle contraction provide information about distance. Keep the distinctions clear: disparity concerns the difference between images, convergence concerns inward turning of the eyes, and accommodation concerns a change in the lens used for focusing.

What keeps perception stable when stimulation changes?

Perceptual constancy means perceiving objects as relatively stable despite changes in sensory stimulation. Movement, viewing angle and illumination can change the information reaching the eyes, yet familiar objects retain a relatively stable appearance.

What is size constancy?

Size constancy is the tendency for perceived size to remain relatively unchanged despite changes in distance and retinal image size. An object's image becomes smaller as it moves farther away. Within limits, however, the object appears about the same size.

When a friend approaches from a distance, the image on the retina grows larger, but the friend's perceived size does not change much. Constancy concerns perceived size, not an unchanging retinal image.

What are shape and brightness constancy?

Shape constancy, also called form constancy, is the stable perceived shape of familiar objects despite changes in their orientation. A dinner plate retains its perceived shape whether its retinal image is circular, elliptical or roughly a short line when viewed edge-on.

Brightness constancy is the tendency to maintain apparent brightness under different illumination. Objects appear stable in whiteness, greyness or blackness despite changes in reflected light. White paper is still perceived as white in room light, and coal remains black in sunlight or room light.

These constancies help explain why changing sensory information does not produce an equally large change in our experience of an object's size, shape or brightness.

Why do visual illusions occur?

An illusion is a misperception arising from misinterpretation of sensory information. A mismatch occurs between a physical stimulus and its perception. Such perception is nonveridical, meaning that it does not accurately represent the stimulus.

Illusions result from external stimulus situations and are experienced more or less by all of us. Some are universal or permanent and do not change with experience or practice. Others seem to vary between individuals and are called personal illusions.

What do geometrical illusions show?

Two horizontal lines labelled A and B have differently oriented curved ends. The lines are equal in length, but A is perceived as shorter than B.

See Fig. 4.13 in your NCERT textbook

In the vertical-horizontal illusion, equal vertical and horizontal lines are perceived differently: the vertical line appears longer. These examples show that physical equality does not guarantee equality in perceived length.

What is apparent movement?

The phi-phenomenon, or apparent movement illusion, occurs when motionless pictures are presented successively at an appropriate rate. Cinema and successively flickering electrical lights illustrate this experience. What is perceived as moving need not itself be a continuously moving object.

Wertheimer identified appropriate brightness, size, spatial gap and temporal contiguity, meaning closeness in time, as important conditions for successive lights to generate motion. Without them, the lights may appear as one point or separate successive points without movement.

Illusions show that people do not always perceive the world as it is. Perception involves construction influenced by stimulus features and experience in an environment.

How do socio-cultural experiences influence perception?

Learning opportunities and cultural experiences affect interpretation. Perceptual habits develop differently across settings, so people may differ in their susceptibility to illusions and their ability to interpret pictures. Susceptibility here means the tendency to experience an illusion.

What do studies of illusions suggest?

Segall, Campbell and Herskovits compared samples from remote African villages and Western urban settings. African participants showed greater susceptibility to the horizontal-vertical illusion, while Western participants showed greater susceptibility to the Muller-Lyer illusion.

The explanation linked forest experience with the overestimation of verticality, such as tall trees. Environments characterised by right angles were linked with underestimating lines marked by enclosure. These findings suggest that habits of perception are learnt differently in different cultural settings.

How does familiarity with pictures matter?

Hudson found that people who had never seen pictures had great difficulty recognising depicted objects and interpreting depth cues such as superimposition, another term for overlapping. Informal instruction at home and habitual exposure to pictures were indicated as necessary to sustain pictorial depth perception.

Sinha and Mishra studied pictorial perception among forest hunters and gatherers, village agriculturists and people living and working in cities. Their studies indicate that picture interpretation is strongly related to cultural experience.

People in general can recognise familiar objects in pictures. However, those less exposed to pictures have difficulty interpreting the actions or events depicted. Recognising an individual object and understanding an entire pictured event therefore need to be distinguished.

Glossary

• Sensation — The initial experience of a stimulus registered by a particular sensory organ.
• Psychophysics — The study of relationships between physical stimuli and the sensations they evoke.
• Absolute threshold — The minimum stimulus value detected on 50 per cent of occasions across trials.
• Difference threshold — The minimum stimulus change producing a noticeable difference on 50 per cent of trials.
• Selective attention — Selection of a limited number of stimuli from the many available for processing.
• Sustained attention — Maintaining attention on an object or event over a longer period of time.
• Divided attention — Allocation of attention to more than one activity at the same time.
• Perception — Recognition, interpretation and construction of meaning from information supplied by the sensory organs.
• Perceptual set — Expectations about a situation that influence what a person perceives within it.
• Figure-ground segregation — Organisation in which a figure stands out distinctly from its surrounding background.
• Monocular cues — Sources of depth information that remain effective when viewing with one eye.
• Retinal disparity — The difference between the images of an object formed on the two retinas.
• Perceptual constancy — Perception of objects as relatively stable despite changes in stimulation of sensory receptors.
• Illusion — A misperception produced by misinterpreting information received through the sensory organs.
• Phi-phenomenon — Apparent movement experienced when motionless pictures are presented successively at an appropriate rate.

Common errors and misconceptions

• Misconception: Sensation already explains what a stimulus means. Correct: Sensation supplies basic experience; perception recognises and interprets it using other psychological processes.
• Misconception: Absolute threshold is fixed for everybody. Correct: It varies considerably between individuals and situations, so detection is assessed across trials.
• Misconception: Difference threshold measures when plain water first tastes sweet. Correct: That illustrates absolute threshold; difference threshold concerns a noticeable change from an existing level of sweetness.
• Misconception: Selective attention and vigilance are identical. Correct: Selection concerns which stimuli receive attention, whereas vigilance concerns maintaining attention for longer durations.
• Misconception: Filter-attenuation theory completely blocks unattended stimuli. Correct: It weakens them, allowing some personally relevant information to reach higher processing occasionally.
• Misconception: Every monocular cue is pictorial. Correct: Motion parallax is a kinetic monocular cue and is not considered pictorial.
• Misconception: Size constancy means the retinal image stays unchanged. Correct: The retinal image changes with distance while perceived size remains relatively stable within limits.
• Misconception: Picture interpretation is unaffected by experience. Correct: Cultural experience and exposure to pictures affect recognition of depicted objects, depth, actions and events.

Exam-style questions with model answers

Q1. Distinguish absolute threshold from difference threshold, including the detection criterion for each. [2 marks]

1. Absolute threshold is the minimum stimulus value detected on 50 per cent of occasions. It concerns detecting the presence of stimulation.
2. Difference threshold is the minimum change producing a noticeable difference on 50 per cent of trials. It concerns distinguishing between stimulus values.

Q2. A runner waits for the starting whistle, a student focuses on a lecture while ignoring noise, and a person looks for a younger sibling among schoolchildren. Identify and explain the three properties of attention illustrated. [3 marks]

1. The runner illustrates alertness, the readiness to deal with a stimulus that is about to appear. The whistle is the awaited stimulus.
2. The student illustrates concentration, focusing awareness on a specific object while excluding others for the moment. The lecture receives this focused awareness.
3. Looking for the sibling illustrates search, finding a specified subset among a larger set. The sibling is sought among the other children.

Q3. Explain filter theory, filter-attenuation theory and multimode theory, giving one separate point for each theory. [3 marks]

1. Filter theory proposes that simultaneous stimuli pass through short-term memory to a filter. Only one passes for higher processing at that moment; others are screened out.
2. Filter-attenuation theory proposes weakening rather than complete blocking. Some personally relevant stimuli can pass through and occasionally produce responses even when weak.
3. Multimode theory allows selection during sensory representation, semantic representation or entry into consciousness. Early selection requires less mental effort than late selection.

Q4. Explain four factors that influence performance on sustained-attention tasks: sensory modality, clarity, temporal uncertainty and spatial uncertainty. [4 marks]

1. Sensory modality concerns the sense receiving the signal. Performance is superior when signals are auditory, received through hearing, compared with visual signals.
2. Clarity concerns the character of stimulation. Intense and long-lasting signals facilitate sustained attention and lead to better performance.
3. Temporal uncertainty concerns when signals occur. Stimuli appearing regularly are attended better than those appearing at irregular intervals.
4. Spatial uncertainty concerns where signals appear. Fixed-location signals are readily attended, while signals appearing at random locations are difficult to attend.

Q5. Explain any five of these Gestalt principles: proximity, similarity, continuity, smallness, symmetry, surroundedness and closure. Give one distinct explanation for each selected principle. [5 marks]

1. Proximity groups objects that are close together in space or time. Their closeness makes them appear to belong together within the visual field.
2. Similarity groups objects with shared characteristics. Similar forms can be seen as belonging together even when all the elements are evenly spaced.
3. Continuity means that objects tend to be grouped when they appear to form a continuous pattern. The perceived organisation follows this continuity.
4. Smallness means that smaller areas tend to be perceived as figures against a larger background. Relative area contributes to figure-ground organisation.
5. Closure means that gaps in stimulation tend to be filled perceptually. We experience a whole object rather than merely its separated parts.

Q6. Explain retinal disparity, convergence and accommodation as sources of information about distance. [3 marks]

1. Retinal disparity is the difference between the two eye images. Large disparity indicates a nearby object, while small disparity indicates a distant one.
2. Convergence is the inward turning of the eyes. Messages about greater inward turning are interpreted as indicating a nearer object.
3. Accommodation changes lens thickness through the ciliary muscle. Information about its contraction provides a distance cue as the eye focuses on nearer objects.

Q7. Explain three perceptual constancies using these situations: an approaching friend's retinal image enlarges; a dinner plate's retinal image changes with viewing angle; white paper reflects different amounts of light in sunlight and room light. [3 marks]

1. Size constancy keeps the friend's perceived size relatively unchanged despite the enlarging retinal image. This stability operates within limits.
2. Shape constancy preserves the familiar plate's perceived shape despite changes in its retinal image caused by different viewing angles.
3. Brightness constancy preserves the paper's apparent whiteness despite different illumination and reflected light. The paper is perceived as white in both situations.

Q8. Study findings show greater horizontal-vertical illusion susceptibility in remote African village samples and greater Muller-Lyer susceptibility in Western urban samples. Forest experience was linked with overestimating verticality; experience of right-angled environments was linked with underestimating lines characterised by enclosure. Hudson found difficulty recognising depicted objects and interpreting pictorial depth among people without previous picture exposure. Sinha and Mishra linked picture interpretation strongly with cultural experience: familiar objects were generally recognised, but those less exposed to pictures struggled with depicted actions and events. Explain five implications of these findings for perception. [5 marks]

1. Susceptibility to a particular illusion can differ across cultural settings. The two samples showed different relative susceptibility to the two illusion figures.
2. Regular experience of verticality in forests was linked with overestimating it. This connects an observed perceptual tendency with features of the experienced environment.
3. Experience of right-angled environments was linked with underestimating lines characterised by enclosure. Perceptual habits can therefore develop differently in different settings.
4. Hudson's finding connects limited picture exposure with difficulty recognising depicted objects and interpreting depth. Pictorial interpretation depends on experience rather than simply having functioning eyes.
5. Sinha and Mishra's finding supports a strong relationship between cultural experience and picture interpretation. Familiar-object recognition should be distinguished from interpreting actions and events in pictures.

Key takeaways

• Sensation supplies basic information, attention selects among stimuli, and perception recognises and constructs their meaning through interacting psychological processes.
• Absolute threshold concerns detecting stimulation; difference threshold concerns detecting change. Both use a 50 per cent criterion across trials.
• Selective attention depends on stimulus features and personal factors, while sustained attention concerns maintaining concentration over longer durations.
• Bottom-up processing begins with parts, top-down processing begins with the whole, and both interact in perception.
• Gestalt principles explain how visual elements are grouped into organised forms and distinguished from their backgrounds.
• Depth perception uses monocular and binocular information to construct three-dimensional experience from flat retinal images.
• Size, shape and brightness constancies preserve relatively stable perception despite changes in distance, orientation or illumination.
• Illusions and cross-cultural studies show that perception reflects stimulus features, expectations, learning and experience with the environment.

Test yourself

Why must absolute threshold be assessed across several trials?

It varies with individuals, situations, bodily conditions and motivational states, so it is defined using detection on 50 per cent of occasions.

How does the fringe of attention differ from its focus?

The focus occupies the centre of awareness; the fringe contains objects or events of which we are only vaguely aware.

What are the three features of automatic processing?

It occurs without intention, takes place unconsciously and involves very little or no thought processes.

What does the principle of closure explain?

We tend to fill gaps in sensory stimulation and perceive a whole object rather than separate parts.

Why is motion parallax not considered a pictorial cue?

It depends on relative movement at different distances, making it a kinetic monocular cue.

What does greater retinal disparity indicate?

A greater difference between the two retinal images is interpreted as indicating a closer object.

Which conditions did Wertheimer identify for apparent movement between successive lights?

Appropriate brightness, size, spatial gap and temporal contiguity of the lights were important for experiencing apparent movement.

How can limited exposure to pictures affect interpretation?

People may have difficulty recognising depicted objects, interpreting depth, or understanding pictured actions and events, depending on their experience.