Class 11 Psychology Chapter 4 Sensory, Attentional and Perceptual Processes Notes in English

1 Knowing the World

Look around your room: table, chair, books, bag, a watch, pictures on the wall. Step outside and there are trees, animals and buildings. You know all of these without any effort. Ask yourself how you know they exist, and the answer is: through your sense organs (eyes, ears and so on). They collect information from the outside world and from inside our own body, and this information is the base of all our knowledge.

But just registering an object is not enough. The object and its qualities (size, shape, colour) must first draw our attention, and the information must then reach the brain, which makes meaning out of it. So our knowledge of the world rests on three processes.

2 Nature and Varieties of Stimulus

Our surroundings contain many kinds of stimuli. Some can be seen (a house), some only heard (music), some smelt (a flower’s fragrance), some tasted (sweets) and some felt by touch (a soft cloth). To deal with them, humans have seven sense organs, also called sensory receptors or information gathering systems, because they gather information from many sources. With these seven organs we register ten different varieties of stimuli, and also their qualities: a light may be bright or dim, yellow or green; a sound may be loud or faint, melodious or distracting.

Note that the skin has separate, specialised receptors for warmth, cold and pain inside it.

3 Sense Modalities

3.1 Functional limitations of sense organs

Our sense organs work only within a limited range. Eyes cannot see things that are very dim or very bright; ears cannot hear very faint or very loud sounds. The same is true of every sense. To be noticed, a stimulus must have an optimal intensity or magnitude. The branch that studies how stimuli are related to the sensations they produce is called psychophysics.

Continuing the sugar test: once the water tastes sweet, keep adding granules. The number of extra granules needed before the water tastes sweeter than before on 50 per cent of occasions is the DL of sweetness.

Thresholds alone do not explain sensation. A sense organ receives the stimulus and turns it into an electrical impulse, which must reach the higher brain centres. So any structural or functional defect or damage in the receptor organ, its neural pathway or the brain area concerned can cause partial or complete loss of sensation.

4 Attentional Processes

Many stimuli hit our senses at the same moment, but we notice only a few. In your classroom there are doors, walls, windows, paintings, desks, students, bags and bottles, yet at one time you focus on just one or two of them.

4.1 Properties of attention

Besides selection, attention has three more properties. All of them need some effort, so attention is also described as “effort allocation”.

(The chapter Summary lists these three as activation, concentration and search; “activation” there means the same readiness as alertness.)

4.2 Focus and fringe

4.3 Types of attention

A process-oriented view divides attention into two types: selective and sustained. When we attend to two different things at the same time, it is called divided attention.

4.4 Selective attention

Our perceptual system has a limited capacity: it can handle only a few stimuli at a moment. Which ones get selected depends on the following factors.

Type of factor	What it is	Examples from the book
External (features of the stimulus)	Size, intensity and motion of stimuli	Large, bright, moving stimuli; novel and moderately complex stimuli; human photographs more than photographs of non-living objects; rhythmic sounds more than spoken narration; sudden and intense stimuli
Internal: motivational	Our biological or social needs	A hungry person notices even a faint smell of food; a student taking an exam focuses on the teacher’s instructions
Internal: cognitive	Interest, attitude and preparatory set	Interesting things are attended to readily; we quickly notice things we feel favourably about

4.5 Theories of selective attention

4.6 Divided attention (Box 4.1)

People drive while talking to a friend, taking a phone call, putting on sunglasses or listening to music. Watch closely and they still give more effort to driving than to the rest. So attention can sometimes go to more than one thing at once, but only when the activities are highly practised. Such activities become almost automatic and need less attention than new or slightly practised ones.

4.7 Sustained attention

Selective attention is about selection; sustained attention is about concentration. Air traffic controllers and radar readers must watch screens for hours. Signals appear unpredictably, and a missed signal may be fatal, so they need a great deal of vigilance.

Factor influencing sustained attention	What helps performance
1. Sensory modality	Performance is better when signals are auditory than when they are visual
2. Clarity of stimuli	Intense and long-lasting stimuli help
3. Temporal uncertainty	Stimuli at regular intervals are attended better than at irregular intervals
4. Spatial uncertainty	Stimuli at a fixed place are attended easily; random locations are hard

4.8 Span of attention (Box 4.2)

The span is measured with an instrument called the tachistoscope. This limited span explains why number plates carry only four digits with a few letters: a traffic policeman can read and note them quickly when a driving rule is broken. Some children do poorly in school simply because of an attention problem, which brings us to ADHD.

4.9 Attention Deficit Hyperactivity Disorder (Box 4.3)

ADHD is a behavioural disorder that is common in children in their primary school years, and boys show it more often than girls. If not managed, the attention problem can continue into adolescence or adulthood.

Treatment	What the book says
Drug Ritalin	Reduces over-activity and distractibility, raises attention and concentration. But it does not “cure”, and may suppress normal growth of height and weight.
Behavioural management programmes	Positive reinforcement, and learning tasks arranged to keep errors low and give quick feedback and success: found quite useful.
Cognitive behavioural training	Rewards for desired behaviour plus training in verbal self-instructions: “stop, think, and then do”. Children learn to shift attention less often and behave reflectively, and this learning stays fairly stable.

5 Perceptual Processes

A sensation alone (a flash of light, a sound, a smell) tells us nothing about where it came from. To make sense of this raw material, we process it further using our learning, memory, motivation, emotions and other psychological processes.

People often build up stimuli in their own way. So perception is not just reading objects as they exist; it is also a construction of objects and events from one’s own point of view. The sub-processes of meaning-making are shown below (Fig. 4.1 of the book).

5.1 Processing approaches in perception

Do we recognise a dog because we first notice its furry coat, four legs, eyes and ears, or do we notice those parts because we have first recognised a dog? Both routes exist.

Studies show that in perception both processes interact to give us an understanding of the world.

6 The Perceiver

Humans are not machines passively receiving stimuli. They are creative beings who understand the world in their own way. Their motivation, expectations, cultural knowledge, past experience, memories, values, beliefs and attitudes all shape perception. Four of these are described in the book.

6.1 Motivation

Our needs and desires strongly affect what we perceive; one way to satisfy a need is to see objects as things that would satisfy it. In experiments, hungry people shown ambiguous pictures saw them as food more often than satiated (non-hungry) people did.

6.2 Expectations or perceptual sets

What we expect to see in a situation shapes what we see. This tendency to see what we expect, even when it does not match reality, is called perceptual familiarisation or perceptual generalisation. If the milkman comes daily at about 5.30 A.M., any knock at that time is perceived as the milkman, even if it is someone else.

6.3 Cognitive styles

6.4 Cultural background and experiences

Study / group	What was found
Hudson: African subjects	People from a pictureless environment could not identify objects in pictures (antelope, spear), failed to see distance in pictures and interpreted them wrongly
Eskimos	Make fine distinctions among many kinds of snow that others cannot notice
Aboriginal groups of the Siberian region	Tell apart dozens of skin colours of reindeer

7 Principles of Perceptual Organisation

Our visual field is made of points, lines and colours, yet we see a bicycle as one object, not as a saddle, wheel and handle lying separately.

7.1 The Gestalt view

The most widely accepted answer to how parts become wholes came from the Gestalt psychologists: prominently Köhler, Koffka and Wertheimer.

• Configuration: a flower pot with flowers is one whole; remove the flowers and the pot is still a whole. Only the configuration has changed.
• Pragnanz: our brain processes always lean towards perceiving a good figure, which is why we see everything in an organised form.
• Figure-ground segregation is the most primitive organisation: words on a page, a painting on a wall, birds in the sky stand out as figures; the page, wall and sky stay behind as ground.

In Rubin’s Vase (Fig. 4.3) you see either a white vase or two black faces looking at each other, never both at once: the figure and ground keep switching.

Figure	Ground (background)
1. Has a definite form	Relatively formless
2. More organised	Less organised
3. Clear contour (outline)	Contourless
4. Stands out	Stays behind the figure
5. Clear, limited, relatively nearer	Unclear, unlimited, away from us

7.2 Gestalt principles (laws) of organisation

Principle	What it says	Book’s example
1. Proximity	Objects close together in space or time are seen as a group	Dots seen as columns (or rows), not as a square pattern (Fig. 4.4)
2. Similarity	Objects with similar features are seen as a group	Evenly spaced circles and squares seen as alternating columns (Fig. 4.5)
3. Continuity	Objects that seem to form a continuous pattern are seen as belonging together	Two lines a-b and c-d crossing, rather than four lines meeting at centre p (Fig. 4.6)
4. Smallness	Smaller areas tend to be seen as figures against a larger background	A black cross rather than a white cross inside the circle (Fig. 4.7)
5. Symmetry	Symmetrical areas are seen as figures against asymmetrical backgrounds	Black symmetrical areas seen as figures on a white background (Fig. 4.8)
6. Surroundedness	Areas surrounded by others are seen as figures	Five figures on white, rather than the word ‘LIFT’ (Fig. 4.9)
7. Closure	We fill gaps and see objects as wholes, not separate parts	Small angles seen as a triangle (Fig. 4.10)

8 Perception of Space, Depth and Distance

The image an object casts on the retina is flat and two-dimensional (left, right, up, down), yet we see three dimensions. This is because we can turn a two-dimensional retinal image into a three-dimensional perception.

We use it daily: judging the distance of an approaching vehicle while driving, or deciding how loudly to call a person walking down the street. Depth is judged from sources of information called cues.

8.1 Monocular cues (psychological cues)

Cue	How it signals distance
Relative size	As an object moves away its retinal image becomes smaller; small-looking objects are seen as farther, bigger-looking ones as closer
Interposition or overlapping	The object partly covered is seen as farther; the one covering it as nearer
Linear perspective	Distant objects look closer together; parallel rail tracks seem to meet at a vanishing point on the horizon. The more lines converge, the farther they look
Aerial perspective	Dust and moisture in the air make distant objects hazy; distant mountains look blue due to scattering of blue light, and seem closer when the air is clear
Light and shade	Highlights and shadows on an object give information about its distance
Relative height	When we expect two objects to be the same size and they are not, the larger appears closer and the smaller farther
Texture gradient	A part of the visual field with greater density of elements is seen as farther (stones look denser further away, Fig. 4.12)
Motion parallax	A kinetic monocular cue, so not a pictorial cue. Distant objects seem to move slowly, near ones fast. From a moving bus, near objects move “against” the bus and far objects move “with” it

8.2 Binocular cues (physiological cues)

9 Perceptual Constancies

As we move around, the information reaching our senses keeps changing, yet we see an object as stable from any position and in any light.

Constancy	Meaning	Example
Size constancy	Perceived size stays about the same despite changes in distance and in retinal image size (within limits)	A friend walking towards you does not seem to grow, though the retinal image gets bigger
Shape (form) constancy	Familiar objects keep their shape despite changes in retinal image due to orientation	A dinner plate looks round whether its image is a circle, an ellipse or almost a short line (edge view)
Brightness constancy	Apparent whiteness, greyness or blackness stays constant under different illumination	White paper looks white in sunlight and room light; coal looks black in both

10 Illusions

Our perceptions are not always veridical (true to reality). Sometimes the sensory information is misread and the percept does not match the physical stimulus.

Illusions come from the external stimulus situation and produce the same experience in everyone, so they are also called “primitive organisations”. They can occur in any sense, but have been studied mostly in vision.

10.1 Geometrical illusions

• Muller-Lyer illusion (Fig. 4.13): line A is seen as shorter than line B though both are equal. Even children experience it, and some studies suggest animals do too.
• Vertical-horizontal illusion (Fig. 4.14): two equal lines, but the vertical one looks longer than the horizontal one.

10.2 Apparent movement illusion (phi-phenomenon)

Films in a cinema and a series of flickering electric lights both create it. It can be studied in the lab by presenting two or more lights in succession. According to Wertheimer, four things about the lights must be just right: brightness, size, the gap in space between them, and the gap in time (temporal contiguity); without these the lights look like one point or separate points one after another, with no movement.

Illusions show that we do not perceive the world exactly as it is; we construct it, partly from stimulus features and partly from our experience of the environment.

11 Socio-Cultural Influences on Perception

Do people in different cultures organise what they perceive in the same way? Psychologists tested this with illusion figures and pictures.

Study	Finding	Explanation
Segall, Campbell and Herskovits: the most extensive study of illusion susceptibility (remote African villages vs Western urban settings)	The horizontal-vertical illusion fooled the African groups more; the Muller-Lyer illusion fooled the Western groups more	Africans living in dense forests often see verticality (tall trees) and learn to overestimate it; Westerners live among right angles and learn to underestimate lines enclosed by arrowheads. Habits of perception are learnt differently in different cultures
Hudson: seminal study in Africa	People who had never seen pictures found it very hard to recognise objects in them and to read depth cues such as superimposition	Informal instruction at home and habitual exposure to pictures are needed to keep the skill of pictorial depth perception
Sinha and Mishra: hunters and gatherers in forests, agriculturists in villages, city employees	Interpretation of pictures is strongly linked to cultural experience	Most people recognise familiar objects in pictures, but those less exposed to pictures struggle to interpret actions or events shown in them

12 Review Questions: Short Answers