CLASS 11 – PSYCHOLOGY

CHAPTER 4 : Sensory, Attentional and Perceptual Processes

1. INTRODUCTION

• Human beings continuously receive information from the environment using their senses.
• This information is processed, interpreted, and given meaning by cognitive systems.
• The process involves three major components:
  1. Sensation – receiving raw information through sensory organs.
  2. Attention – selecting relevant information for processing.
  3. Perception – interpreting and meaningfully organizing sensory data.
• These three processes help us understand our surroundings, plan actions, and adapt to challenges.
• Without sensory input, attention control, and perceptual organization, we would not be able to recognize objects, respond to danger, or navigate the environment.
• Perception is an active, constructive process influenced by biological, psychological, and socio-cultural factors.

2. NATURE AND VARIETIES OF STIMULUS

A stimulus is any form of energy or information that activates a sense organ.

Characteristics of Stimuli

• Intensity – strength of the stimulus (e.g., loud vs. soft sound).
• Duration – how long the stimulus lasts.
• Frequency – repetition of the stimulus.
• Complexity – simple vs. complicated stimulus patterns.
• Novelty – new or unexpected stimuli attract attention more.
• Meaningfulness – relevant or personally significant stimuli are more noticeable.

Types of Stimuli

1. Distal Stimuli

• Actual objects or events in the external world.
• Example: A tree, an animal, a moving car.

2. Proximal Stimuli

• The sensory patterns reaching our sense organs.
• Example: Light entering the retina, sound waves reaching the eardrum.

3. Energetic Stimuli

• Pressure, heat, sound waves, chemical molecules.

4. Psychosocial Stimuli

• Smiles, gestures, language, social cues that influence perception.

Thresholds of Sensation

1. Absolute Threshold

• Minimum energy required for a person to detect a stimulus 50% of the time.
• Example: A candle seen at 30 miles on a clear night.

2. Difference Threshold / JND (Just Noticeable Difference)

• Minimum difference between two stimuli required to detect change.
• Based on Weber’s Law – change must be proportionate to the original stimulus.

3. Signal Detection

• Detection depends on:
  • sensitivity of sensory system
  • decision-making (experience, expectations, motivation)

3. SENSE MODALITIES

Humans have five major sensory systems:

A. Vision (Seeing)

Stimulus: Light waves

• Eyes convert light energy into neural impulses through transduction.
• Retina contains rods (low light) and cones (color).
• Visual pathways send information to the brain’s occipital lobe.

Key Processes

• Adaptation
• Color perception
• Depth and movement perception

B. Audition (Hearing)

Stimulus: Sound waves

• Ear structures transmit vibrations to the cochlea.
• Hair cells convert mechanical energy into neural signals.
• Brain interprets pitch, volume, and direction of sound.

C. Olfaction (Smell)

Stimulus: Chemical molecules in air

• Receptors in nasal cavity send signals to the olfactory cortex.
• Smell is closely linked to emotion and memory (limbic system).

D. Gustation (Taste)

Stimulus: Chemical molecules in food

• Tongue has taste buds for five basic tastes:
  • sweet
  • salty
  • sour
  • bitter
  • umami
• Taste combines with smell and texture to create flavour.

E. Somatosensory System (Touch, Pain, Temperature, Body Position)

• Receptors in skin detect pressure, vibration, temperature, pain.
• Proprioceptors provide body position and movement information.
• Helps maintain posture, coordination, and motor control.

4. ATTENTIONAL PROCESSES

Attention is the process of selecting and focusing on specific environmental information while ignoring others.

Nature of Attention

• Selective – we choose certain stimuli and ignore others.
• Limited capacity – cannot attend to everything at once.
• Dynamic – constantly shifts depending on needs and environment.
• Goal-directed and stimulus-driven at the same time.

Types of Attention

1. Selective Attention

• Focusing on one stimulus while filtering out irrelevant ones.
• Example: listening to a teacher in a noisy classroom.

2. Sustained Attention

• Maintaining attention over time.
• Required in driving, studying, or watching a lecture.

3. Divided Attention

• Processing multiple things simultaneously.
• Example: walking and talking.

4. Shifting Attention

• Moving attention from one task to another (task switching).

Factors Influencing Attention

A. External Factors

• Intensity, size, contrast, novelty, movement
• Example: bright light attracts immediate attention.

B. Internal Factors

• Interests
• Motivations
• Emotional state
• Past experiences
• Expectations

Theories of Attention

1. Filter Theory (Broadbent)

• Information is filtered early; only selected information is processed deeply.

2. Attenuation Theory

• Unattended information is not completely blocked, just weakened.

3. Resource Allocation Theory

• Attention depends on mental resources.
• More difficult tasks require more attention.

5. PERCEPTUAL PROCESSES

Perception is the process of organizing and interpreting sensory input to make sense of the environment.

Steps of Perception

1. Selection

• Choosing which sensory information to consider.

2. Organization

• Grouping information based on features and patterns.

3. Interpretation

• Assigning meaning to organized data.

Characteristics of Perception

• Active process
• Influenced by expectations
• Based on past experiences
• Constructive and meaningful
• Can be inaccurate or biased

6. PRINCIPLES OF PERCEPTUAL ORGANISATION

Based on Gestalt psychology, which states:
“The whole is more than the sum of its parts.”

Gestalt Principles

1. Figure–Ground

• We separate objects (figure) from background (ground).
• Example: reading black letters on a white page.

2. Similarity

• Similar elements are grouped together.

3. Proximity

• Near objects appear as a group.

4. Continuity

• We perceive patterns as continuous rather than broken.

5. Closure

• Brain fills missing gaps to complete a figure.

6. Symmetry

• Balanced forms are perceived as whole.

7. Common Fate

• Moving objects in the same direction are grouped together.

7. PERCEPTION OF SPACE, DEPTH AND DISTANCE

Humans perceive three-dimensional world through depth cues.

A. Monocular Cues (One eye)

• Interposition – nearer objects block farther ones.
• Size – closer objects appear larger.
• Texture Gradient – nearer objects appear clearer.
• Linear Perspective – parallel lines appear to meet at distance.
• Aerial Perspective – distant objects look hazy.
• Light and Shadow – gives 3D appearance.
• Motion Parallax – closer objects move faster when we move.

B. Binocular Cues (Two eyes)

1. Retinal Disparity

• Difference between images on two retinas gives depth.

2. Convergence

• Eyes turn inward when object is near.

8. ILLUSIONS

Illusions are misinterpretations of actual stimuli.
They occur when perception does not match reality.

Types of Illusions

1. Physical Illusions

• Due to physical factors like light, shadow, refraction.

2. Psychological Illusions

• Due to perceptual tendencies and brain interpretation.

3. Cultural Illusions

• Perception shaped by cultural experiences.

Famous Visual Illusions

• Müller-Lyer illusion – arrowheads distort length perception.
• Ponzo illusion – converging lines create depth-inducing distortion.
• Hering and Zollner illusions – lines appear tilted or bending.
• Moon illusion – moon looks larger near horizon.

9. SOCIO-CULTURAL INFLUENCES ON PERCEPTION

Perception is not purely biological; it is shaped by society and culture.

Factors

1. Cultural Background

• Different cultures perceive shapes, colors, and depth cues differently.
• Example: Tribal societies are less prone to the Müller-Lyer illusion due to non-carpentered environments.

2. Social Conditioning

• Values and norms guide what we notice and ignore.

3. Past Experiences

• Experience with technology, media, environment influences perceptual accuracy.

4. Language

• Labels and categories in a language shape how we classify objects.

5. Learning and Education

• Educated individuals may process information more analytically.

6. Motivation and Emotions

• Hungry people perceive food-related cues more quickly.
• Fear or anger biases perception of neutral stimuli.

10. CONCLUSION

• Sensory, attentional, and perceptual processes help individuals interpret the world.
• Sensation provides raw data; attention filters important information; perception organizes and interprets it.
• Understanding these processes explains why people perceive the same stimulus differently.
• Perception is influenced by biological, psychological, and socio-cultural factors.
• Depth perception, perceptual organization, and illusions reveal the complexity of the brain’s interpretation mechanisms.
• These processes help humans survive, learn, behave, and interact effectively in daily life.