NCERT Solutions for Class 11 Psychology Chapter 4: Sensory, Attentional and Perceptual Processes

Chapter at a glance

Exercise Questions

Answer

Our sense organs can respond only to stimuli within a certain range of intensity or magnitude:

1. Absolute threshold (AL): the minimum value of a stimulus needed to be noticed 50 % of the time. Stimuli weaker than this are not perceived (e.g. a very faint sound or a drop of sugar in a bucket of water).
2. Upper limit: extremely intense stimuli (very bright light, very loud sound) cannot be sensed properly and may cause pain or damage.
3. Difference threshold (DL) / Just Noticeable Difference (JND): the smallest difference between two stimuli that can be detected; smaller differences go unnoticed.
4. Range of sensitivity: the human eye sees only wavelengths of about 380–780 nm (visible light), and the ear hears sounds of about 20–20,000 Hz; we cannot sense ultraviolet, infrared, ultrasound, etc.
5. Sense organs may also adapt to constant stimuli and become less sensitive, and they deteriorate with age.

Sense organs work only within limits: stimuli below the absolute threshold or above the upper limit are not sensed, differences smaller than the JND go unnoticed, and each sense has a fixed range (e.g. 380–780 nm light, 20–20,000 Hz sound).

Answer

Attention is the process of selecting certain stimuli from the many present in the environment and focusing on them while ignoring others.

Properties

1. Selection: choosing a few stimuli from the many available (e.g. listening to a friend in a noisy room).
2. Alertness: readiness of the individual to deal with incoming stimuli (e.g. a sprinter waiting for the starting signal).
3. Concentration: focusing awareness on particular objects while excluding others.
4. Span of attention: the number of objects that can be attended to at one time (about 7 ± 2 items).
5. Attention has a focus (the centre, most clearly perceived) and a margin (objects less clearly perceived).

Attention is selecting and focusing on certain stimuli while ignoring others; its properties are selection, alertness, concentration and span (with a focus and margin).

Answer

Determinants of selective attention

1. External factors (features of the stimulus): size (larger objects attract more attention), intensity (bright, loud), motion, novelty, complexity, contrast and repetition. Advertisers use these.
2. Internal factors (features of the person):
   • Motivational factors — needs and interests (a hungry person notices food smells);
   • Cognitive factors — interest, attitude and preparatory set (expectation).

Selective vs sustained attention

Sustained attention depends on sensory modality, clarity of stimuli, temporal uncertainty and spatial uncertainty.

Determinants are external (size, intensity, motion, novelty, complexity) and internal (motives, interests, set). Selective attention is choosing which stimuli to attend to; sustained attention is maintaining attention for a long time (vigilance).

Answer

Gestalt psychologists (Wertheimer, Köhler, Koffka) proposed that we perceive the world as organised wholes (gestalts) rather than as separate parts — “the whole is different from the sum of its parts.” The brain organises sensations into meaningful patterns according to principles:

1. Figure and ground: we perceive an object (figure) standing out against a background (ground).
2. Proximity: objects close together are seen as a group.
3. Similarity: similar objects are grouped together.
4. Continuity: we perceive continuous lines or patterns.
5. Closure: we fill in gaps to see incomplete figures as complete.
6. Smallness / symmetry / surroundedness: smaller areas and symmetrical regions tend to be seen as figures.

These principles reflect the tendency to perceive a good form (Prägnanz).

Perception is organised into meaningful wholes — the whole differs from the sum of its parts — through principles like figure–ground, proximity, similarity, continuity, closure and symmetry.

Answer

Space perception is the perception of the size, shape, distance and direction of objects in three-dimensional space, though the image on the retina is two-dimensional.

• We infer the third dimension (depth) using cues:
  • Monocular (psychological) cues — available with one eye: relative size, interposition (overlap), linear perspective, aerial perspective, texture gradient, light and shade, height in the visual field, motion parallax.
  • Binocular (physiological) cues — require both eyes: retinal disparity, convergence and accommodation.
• The brain combines these cues with past experience and learning to judge distance and depth.
• Perceptual constancies (size, shape, brightness) help maintain stable perception.

By using monocular cues (relative size, interposition, perspective, texture gradient, motion parallax) and binocular cues (retinal disparity, convergence, accommodation), combined with experience, the brain converts the 2-D retinal image into 3-D perception.

Answer

Monocular cues (psychological cues, used by artists):

1. Relative size: smaller images are perceived as farther away.
2. Overlap (interposition): an object covering another is seen as nearer.
3. Linear perspective: parallel lines appear to converge in the distance (railway tracks).
4. Aerial perspective: distant objects look hazy or bluish.
5. Light and shade: shadows give depth.
6. Texture gradient: texture becomes finer and denser with distance.
7. Height in the plane: objects higher in the visual field appear farther.
8. Motion parallax: when we move, near objects seem to move faster and opposite, far objects slower.

Binocular cues (physiological, need both eyes):

1. Retinal disparity: each eye receives a slightly different image; the brain combines them; greater disparity means a nearer object.
2. Convergence: eyes turn inward to look at near objects; the brain uses the muscle tension as a cue.
3. Accommodation: the ciliary muscles change the shape of the lens to focus on near objects; this signals distance (for short distances).

Binocular cues are especially important for judging depth of nearby objects.

Monocular cues: relative size, overlap, linear and aerial perspective, light and shade, texture gradient, height in plane, motion parallax. Binocular cues — retinal disparity, convergence and accommodation — give precise depth information for near objects.

Answer

Illusions are misperceptions of real stimuli — the perception does not correspond to the actual physical stimulus (non-veridical perception). They occur because:

1. Our perceptual system uses cues and strategies (perspective, context, constancy) that usually work but can be misled by certain arrangements (e.g. the Müller-Lyer illusion, where lines of equal length look unequal due to arrow-heads).
2. Misinterpretation of sensory information by the brain.
3. Apparent motion — e.g. the phi phenomenon, where lights flashing in sequence seem to move (used in neon signs and cinema).
4. Past experience and expectations influence how we interpret stimuli.
5. Cultural factors: some illusions are universal, others culture-specific — people living in “carpentered” environments (rectangular buildings) are more susceptible to the Müller-Lyer illusion.

Because the brain misinterprets sensory information using cues, context and past experience that are misleading in certain arrangements (Müller-Lyer, phi phenomenon); some illusions are universal, others culture-specific.

Answer

1. Familiarity: culture determines which stimuli are familiar and salient. For example, people from forest cultures perceive depth cues in 2-D pictures differently.
2. Habits of perceiving: people living in “carpentered” environments with straight lines and right angles are more susceptible to the Müller-Lyer illusion than people living in rural areas with round huts (Segall, Campbell and Herskovits).
3. Language and categorisation: cultures with more words for colours or snow perceive finer distinctions.
4. Pictorial depth perception: children from cultures without exposure to pictures and perspective may not see depth in 2-D drawings (Hudson’s studies in Africa).
5. Social values and expectations — what is considered beautiful, important or threatening — influence what we notice.

Culture shapes familiarity with and salience of stimuli, perceptual habits (e.g. Müller-Lyer susceptibility in carpentered environments), categorisation through language, pictorial depth perception and values that direct attention.

Topic checklist

• Sense modalities and their limits
• Attention: properties, selective, divided and sustained
• Gestalt principles of perceptual organisation
• Space and depth perception: monocular and binocular cues
• Illusions and socio-cultural influences

Total questions answered: 8 of 8