Sensory, Attentional Perceptual and Processes Class 11 Psychology Notes


  • These organs collect information not only from the external world, but also from our own body.
  • The information collected by our sense organs forms the basis of all our knowledge.
  • in order to be registered, the objects and their qualities must be able to draw our attention.
  • The  registered information must also be sent to the brain that constructs some meaning out of them.
  • our knowledge of the world around us depends on three basic processes, called sensation, attention, and perception.


  • We have very specialised sense organs to dealwith these different stimuli.
  • The sense organs are also known as sensory receptors or information gathering systems, because they receive or gather information from a variety of sources.
  • these sense organs collect information from the external world.
  • Specialised receptors of warmth, cold, and pain are found inside our skin.
  • we have also got two deep senses. They are called kinesthetic and vestibular systems.
  • They provide us with important information about our body position and movement of body parts related to each other.
  • With these seven sense organs, we register ten different variety of stimul
  • These different qualities of stimuli are also registered by our sense organs.


  • The initial experience of a stimulus or an object registered by a particular sense organ is called sensation.
  • It is a process through which we detect and encode a variety of physical stimuli.
  • Sensation also refers to immediate basic experiences of stimulus attributes, such as “hard”, “warm”, “loud”, and “blue”, which result from appropriate stimulation of a sensory organ.
  • Each sense organ is highly specialised for dealing with a particular kind of information. Hence, each one of them is known as a sense modality.

Functional Limitations of Sense Organs

  • The relationship between stimuli and the sensations they evoke has been studied in a discipline, called psychophysics.
  • The minimum value of a stimulus required to activate a given sensory system is called absolute threshold or absolute limen (AL).
  • It may be noted that the AL is not a fixed point; instead it varies considerably across individuals and situations depending on the people’s organic conditions and their motivational states.
  • Hence, we have to assess it on the basis of a number of trials.
  • As it is not possible for us to notice all stimuli, it is also not possible to differentiate between all stimuli.
  • In order to notice two stimuli as different from each other, there has to be some minimum difference between the value of those stimuli.
  • The smallest difference in the value of two stimuli that is necessary to notice them as different is called difference threshold or difference limen (DL).
  • difference threshold is the minimum amount of change in a physical stimulus that is capable of producing a  sensation difference on 50 per cent of the trials.
  • Sensory processes do not depend only on the stimulus characteristics.
  • Sense organs and the neural pathways connecting them to various brain centers also play a vital role in this process.
  • A sense organ receives the stimulus and encodes it as an electrical impulse.
  • Any structural or functional defect or damage in the receptor organ, its neural pathway, or the concerned brain area may lead to a partial or complete loss of sensation.

Visual Sensation

  • we use visual approximately 80 per cent of our transactions with the external world.
  • Audition and other senses also contribute significantly to information gathering from the external world.
  • Visual sensation starts when light enters the eyes and stimulates our visual receptors.
  • Our eyes are sensitive to a spectrum of light, the wavelength of which ranges from 380 nm to 780 nm (nm refers to nanometer, which is one billionth of a meter).
  • No sensation is registered beyond this range of light.

Light Adaptation

  • Light adaptation refers to the process of adjusting to bright light after exposure to dim light.
  • This process takes nearly a minute or two.
  • dark adaptation refers to the process of adjusting to a dimly illuminated environment after exposure to bright light.
  • This may take half an hour or even longer depending on the previous level of exposure of the eye to light.
  • There are certain ways in which these processes can be facilitated. An interesting activity is given below to demonstrate this process to you.

Photochemical Basis of Light and Dark Adaptation

  • According to the classical view, light and dark adaptations occur due to certain photochemical processes.
  • The rods have a photo-sensitive chemical substance, called rhodopsin or visual purple.
  • By the action of light the molecules of this chemical substance get bleached or broken down.
  • Under such  conditions the light adaptation takes place in the eyes.
  • The dark adaptation is achieved by the removal of light, and thereby allowing for restorative processes to regenerate the pigment in the rods with the help of vitamin A.
  • The regeneration of rhodopsin in rods is a time consuming process.
  • That is why dark adaptation is a slower process than light adaptation.
  • It has been found that people who suffer from vitamin A deficiency do not achieve dark adaptation at all, and find it really difficult to move in the dark.
  • This condition is generally known as night blindness.
  • A parallel chemical believed to be found in cones is known as iodopsin.


  • The process through which certain stimuli are selected from a group of others is generally referred to as attention.
  • Alertness refers to an individual’s readiness to deal with stimuli that appear before her/him.
  • Concentration refers to focusing of awareness on certain specific objects while excluding others for the moment.
  • Attention in this sense refers to “effort allocation”.
  • Attention has a focus as well as a fringe.
  • When the field of awareness is centered on a particular object or event, it is called focus or the focal point of attention.
  • On the contrary, when the objects or events are away from the center of awareness and one is only vaguely
    aware of them, they are said to be at the fringe of attention.

Selective Attention

  • Selective attention is concerned mainly with the selection of a limited number of stimuli or objects from a large number of stimuli.
  • Perceptual system has a limited capacity to receive and process information.
  • This means that it can deal only with a few stimuli at a given moment of time.
  • Psychologists have identified a number of factors that determine the selection of stimuli.

Factors Affecting Selective Attention

  • Studies indicate that human photographs are more likely to be attended to than the photographs of inanimate objects.
  • Sudden and intense stimuli have a wonderful capacity to draw attention.
  • Internal factors lie within the individual.
  • Objects or events, which appear interesting, are readily attended by individuals.
  • Preparatory set generates a mental state to act in a certain way and readiness of the individual to respond
    to one kind of stimuli and not to others.

Theories of Selective Attention

Filter Theory

  • Filter theory was developed by Broadbent . According to this theory, many stimuli simultaneously enter our receptors creating a kind of “bottleneck” situation.
  • Moving through the short-term memory system, they enter the selective filter, which allows only one
    stimulus to pass through for higher levels of processing.
  • Other stimuli are screened out at that moment of time.
  • we become aware  of only that stimulus, which gets access through the selective filter.
  • Filter-attenuation theory was developed by Triesman by modifying Broadbent’s theory.
  • This theory proposes that the stimuli not getting access to the selective filter at a given moment of time are not completely blocked.

Multimode theory

  • Multimode theory was developed by Johnston and Heinz
  • This theory believes that attention is a flexible system that allows selection of a stimulus over others at
    three stages.
  • At stage one the sensory representations of stimuli are constructed; at stage two the semantic representations are constructed; and at stage three the sensory and semantic representations enter the consciousness.
  • It is also suggested that more processing requires more mental effort.

Sustained Attention

  • While selective attention is mainly concerned with the selection of stimuli, sustained attention is concerned with concentration.
  • It refers to our ability to maintain attention on an object or event for longer durations.
  • It is also known as “vigilance”.
  • The occurrence of signals in such situations is usually unpredictable, and errors in detecting signals may be fatal.
  • a great deal of vigilance is required in those situations.

Factors Influencing Sustained Attention

  • Performance is found to be superior when the stimuli are auditory than when they are visual.
  • Intense and long lasting stimuli facilitate sustained attention and result in better performance.
  • Temporal uncertainty is a third factor. When stimuli appear at regular intervals of time they are attended better than when they appear at irregular intervals.
  • Spatial uncertainty is a fourth factor. Stimuli that appear at a fixed place are readily attended, whereas those that appear at random locations are difficult to attend.


  • In order to make sense out of the raw material provided by the sensory system, we process it further.
  • The process by which we recognise, interpret or give meaning to the information provided by sense organs is
    called perception.
  • In interpreting stimuli or events, individuals often construct them in their own ways.
  • perception is not merely an interpretation of objects or events of the external or internal world as they exist, instead it is also a construction of those objects and events from one’s own point of view.
  • The process of meaning-making involves certain sub-processes.

Processing Approaches in Perception

  • The idea that recognition process begins from the parts, which serve as the basis for the recognition of the whole is known as bottom-up processing.
  • The notion that recognition process begins from the whole, which leads to identification of its various components is known as topdown processing.
  • The bottom-up approach lays emphasis on the features of stimuli in perception, and considers perception as a process of mental construction.
  • The top-down approach lays emphasis on the perceiver, and considers perception as a process of recognition or identification of stimuli.
  • in perception both the processes interact with each other to provide us with an understanding of the world.


  • Human beings are not just mechanical and passive recipients of stimuli from the external world.
  • They are creative beings, and try to understand the external world in their own ways.
  • In this process their motivations and expectations, cultural knowledge, past experiences, and memories as well as values, beliefs, and attitudes play an important role in giving meaning to the external world


  • The needs and desires of a perceiver strongly influence her/his perception.
  • People want to fulfil their needs and desires through various means.
  • One way to do this is to perceive objects in a picture as something that will satisfy their need.
  • Experiments were conducted to examine the influence of hunger on perception.

Expectations or Perceptual Sets

  • The expectations about what we might perceive in a given situation also influence our perception.
  • The phenomenon of perceptual familiarisation or perceptual generalisation reflects a strong tendency to see what we expect to see even when the results do not accurately reflect external reality

Cognitive Styles

  • Cognitive style refers to a consistent way of dealing with our environment.
  • It significantly affects the way we perceive the environment.
  • Field dependent people perceive the external world in its totality, i.e. in a global or holistic manner
  • field independent people perceive the external world by breaking it into smaller units, i.e. in an analytic or differentiated manner.

Cultural Background and Experiences

  • Different experiences and learning opportunities available to people in different cultural settings also influence their perception.
  • People coming from a pictureless environment fail to recognise objects in pictures.
  • Hudson studied the perception of pictures by African subjects, and noted several difficulties.
  • The studies indicate that the perceiver plays a key role in the process of perception.
  • People process and interpret stimuli in their own ways depending on their personal, social and cultural conditions.


  • The process of organising visual field into meaningful wholes is known as form perception.
  • According to Gestalt psychologists, we perceive different stimuli not as discrete elements, but as an organised
    “whole” that carries a definite form.
  • They believe that the form of an object lies in its whole, which is different from the sum of their parts.
  • The Gestalt psychologists also indicate that our cerebral processes are always oriented towards the perception of a good figure or pragnanz.
  • That is the reason why we perceive everything in an organised form.
  • Figure has a definite form, while the background is relatively formless.
  • Figure is more organised as compared to its background.
  • Figure has a clear contour (outline), while the background is contourless.
  •  Figure stands out from the background, while the background stays behind the figure.
  • Figure appears more clear, limited, and relatively nearer, while the background appears relatively unclear, unlimited, and away from us.
  • The discussion presented above indicates that human beings perceive the world in organised wholes rather than in discrete parts.
  • The Gestalt psychologists have given us several laws to explain how and why different stimuli in our visual field are organised into meaningful whole objects

The Principle of Proximity

  • Objects that are close together in space or time are perceived as belonging together or as a group

The Principle of Similarity

  • Objects that are similar to one another and have similar characteristics are perceived as a group.

The Principle of Continuity

  • This principle states that we tend to perceive objects as belonging together if they appear to form a continuous pattern

The Principle of Smallness

  • According to this principle, smaller areas tend to be seen as figures against a larger background.

The Principle of Symmetry

  • This principle suggests that symmetrical areas tend to be seen as figures against asymmetrical backgrounds.

The Principle of Surroundedness

  • According to this principle, the areas surrounded by others tend to be perceived as figures

The Principle of Closure

  • We tend to fill the gaps in stimulation and perceive the objects as whole rather than their separate parts


  • The visual field or surface in which things exist, move or can be placed is called space.
  • The space in which we live is organised in three dimensions.
  • We perceive not only the spatial attributes of various objects, but also the distance between the objects found in this space
  • The process of viewing the world in three dimensions is called distance or depth perception.
  • Depth perception is important in our daily life. For example, when we drive, we use depth to assess the  distance of an approaching automobile, or when we decide to call a person walking down the street, we determine the loudness with which to call.
  • In perceiving depth, we depend on two main sources of information, called cues

Monocular Cues

  • Monocular cues of depth perception are effective when the objects are viewed with only one eye.
  • These cues are often used by artists to induce depth in two dimensional paintings.
  • Hence, they are also known as pictorial cues.

Relative Size

  • The size of retinal image allows us to judge distance based on our past and present experience with similar objects.
  • As the objects get away, the retinal image becomes smaller and smaller.
  • We tend to perceive an object farther away when it appears small, and closer when it appears bigger.

Interposition or Overlapping

  • These cues occur when some portion of the object is covered by another object.
  • The overlapped object is considered farther away, whereas the object that covers it appears nearer.

Linear Perspective

  • This reflects a phenomenon by which distant objects appear to be closer together than the nearer objects.

Aerial Perspective

  • The air contains microscopic particles of dust and moisture that make distant objects look hazy or blurry.
  • This effect is called aerial perspective

Light and Shade

In the light some parts of
the object get highlighted, whereas some parts
become darker. Highlights and shadows
provide us with information about an object’s

Relative Height

  • Larger objects are perceived as being closer to the viewer and smaller objects as being farther away.
  • When we expect two objects to be the same size and they are not, the larger of the two will appear closer and the smaller will appear farther away.

Texture Gradient

  • It represents a phenomenon by which the visual field having more density of elements is seen farther away. In the

Binocular Cues

Retinal or Binocular Disparity

  • Retinal disparity occurs because the two eyes have different locations in our head.
  • They are separated from each other horizontally by a distance of about 6.5 centimeters.
  • Because of this distance, the image formed on the retina of each eye of the same object is slightly different.
  • This difference between the two images is called retinal disparity.
  • The brain interprets a large retinal disparity to mean a close object and a small retinal disparity to  mean a distant object, as the disparity is less for distant objects and more for the near objects.


  • When we see a nearby object our eyes converge inward in order to bring the image on the fovea of each eye.
  • A group of muscles send messages to the brain regarding the degree to which eyes are turning inward, and these messages are interpreted as cues to the perception of depth.
  • The degree of convergence decreases as the object moves further away from the observer.
  •  The more your eyes turn inward or converge, the nearer the object appears in space.


  • Accommodation refers to a process by which we focus the image on the retina with the help of ciliary muscle.
  • These muscles change the thickness of the lens of the eye.
  • As the object moves nearer, the muscle contracts and the thickness of the lens increases.
  • The Signal about the degree of contraction of the muscle is sent to the brain, which provides the cue for distance.


  • The sensory information that we receive from our environment constantly changes as we move around
  • Perception of the objects as relatively stable in spite of changes in the stimulation of sensory receptors is called
    perceptual constancy

Size Constancy

  • The size of an image on our retina changes with the change in the distance of the object from the eye.
  • The tendency for the perceived size of objects to remain relatively unchanged with changes in their distance from the observer and the size of the retinal image is called size constancy.

Shape Constancy

  • In our perceptions the shapes of familiar objects remain unchanged despite changes in the pattern of retinal image resulting from differences in their orientation

Brightness Constancy

  • Visual objects not only appear constant in their shape and size, they also appear constant in their degree of whiteness, greyness, or blackness even though the amount of physical energy reflected from them changes
  • our experience of brightness does not change in spite of the changes in the amount of reflected light
    reaching our eyes.
  • The tendency to maintain apparent brightness constant under different amount of illumination is called brightness constancy


  • Our perceptions are not always veridical.
  • The misperceptions resulting from misinterpretation of information received by our sensory organs are generally known as illusions.
  • The result from an external stimulus situation and generate the same kind of experience in each individual.
  • That is why illusions are also called “primitive organisations”.
  • illusions can be experienced by the stimulation of any of our senses, psychologists have studied them more
    commonly in the visual than in other sense modalities.

Geometrical Illusions

  • the Muller-Lyer illusion has been shown.
  • All of us perceive line A as shorter than line B, although both the lines are equal.
  • This illusion is experienced even by children.
  • There are some studies that suggest that even animals experience this illusion more or less like us.
  • Although both the lines are equal, we perceive the vertical line as longer than the horizontal line

Apparent Movement Illusion

  • This illusion is experienced when some motionless pictures are projected one after another at an appropriate rate.
  • This illusion is referred to as “phi-phenomenon”
  • This phenomenon can be experimentally studied with the help of an instrument by presenting two or more lights in a succession.
  • For the experience of  this illusion, Wertheimer had reported the presence of appropriate level of brightness, size, spatial gap, and temporal contiguity of different lights to be important
  • Experience of illusions indicates that people do not always perceive the world as it is; instead they engage in its construction, sometimes based on the features of stimuli and sometimes based on their experiences in
    a given environment.


  • Several psychologists have studied the processes of perception in different sociocultural settings
  • It was found that African subjects showed greater susceptibility to horizontal-vertical illusion, whereas Western subjects showed greater susceptibility to Muller-Lyer illusion.
  • Living in dense forests the African subjects regularly experienced verticality and developed a tendency to overestimate it.
  • The Westerners, who lived in an environment characterised by right angles, developed a tendency to underestimate the length of lines characterised by enclosure
  • This conclusion has been confirmed in several studies.
  • It suggests that the habits of perception are learnt differently in different cultural settings.
  • Hudson did a seminal study in Africa, and found that people, who had never seen pictures, had great difficulty in recognising objects depicted in them and in interpreting depth cues
  • It was indicated that informal instruction in home and habitual exposure to pictures were necessary to sustain the skill of pictorial depth perception.
  • Sinha and Mishra have carried out several studies on pictorial perception using a variety of pictures with people from diverse cultural settings,
  • . Their studies indicate that interpretation of pictures is strongly related to cultural experiences of people.
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