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Since childhood, we have been taught that humans possess 5 types of senses- sight, hearing, touch, taste, and smell. These senses not only help us observe the world around us, but also enable us to survive. This unit on sensory, attentional, and perceptual will introduce you to various receptors and discuss the process of attention, its types, the process of perception, and its socio-cultural influences.
Contents
- 1 Introduction
- 2 Knowing the World
- 3 Nature and Varieties of Stimulus
- 4 Sense Modalities
- 5 Attentional Process
- 6 Perceptual Process
- 7 Approaches to Perception
- 8 The Perceiver
- 9 Principles of Perceptual Organisation
- 10 Perception of Space, Depth, and Distance
- 11 Perceptual Constancies
- 12 Illusions
- 13 Socio-Cultural Influences on Perception
- 14 Important Definition in NCERT Notes Class 11 Psychology Chapter 4: Sensory, Attentional, and Perceptual Processes
- 15 FAQs
Explore Notes of Class 11 Psychology
Introduction
Some of our sensory receptors are clearly visible, while others are located inside the body and cannot be observed without the help of mechanical or electrical instruments. For example, eyes, nose, and ears are our external sensory receptors, while chemoreceptors, osmoreceptors, and stretch receptors are some important internal receptors. These receptors collect and process sensory information, ultimately providing us with a better understanding of the physical world.
Knowing the World
We live in a world filled with a variety of objects, people, and events, like furniture, books, utensils, trees, and buildings. We recognize them effortlessly through daily experience. Our knowledge of these objects comes through our sense organs (e.g., eyes, ears), which:
- Collect information from both the external environment and our body
- Register object features like size, shape, and colour
- Require these features to draw attention to be noticed
The collected information is sent to the brain, which gives it meaning. This process involves three interrelated components:
- Sensation – detecting stimuli
- Attention – focusing on relevant stimuli
- Perception – interpreting and understanding the input
Together, these form the foundation of cognition.
Nature and Varieties of Stimulus
The external environment around us contains a wide variety of stimuli:
- Some can be seen (e.g., a house)
- Some can be heard (e.g., music)
- Some can be smelled (e.g., the fragrance of a flower)
- Some can be tasted (e.g., sweets)
- Some can be touched (e.g., the softness of a cloth)
Human beings have seven specialised sense organs, also known as sensory receptors. Receptors for warmth, cold, and pain are located inside the skin.
The Five External Sense Organs are:
- Eyes
- Ears
- Nose
- Tongue
- Skin
Two deep senses are:
- Kinesthetic system: provides information about the movement of body parts in relation to each other
- Vestibular system: provides information about body position
With these seven sense organs, we register ten different varieties of stimuli. For example:
- You may notice whether a light is bright or dim, or whether it is yellow, red, or green.
- With sound, you may notice whether it is loud or faint, or whether it is melodious or distracting.
Sense Modalities
Sense organs provide direct information about the external and internal worlds. The initial experience registered by a specific sense organ is called sensation, which involves detecting and encoding physical stimuli. Each sense organ is specialised for a particular type of stimulus and is known as a sense modality.
Functional Limitations of Sense Organs
Sense organs have the following limits.
- Eyes cannot detect very dim or very bright light.
- Ears cannot hear very faint or very loud sounds.
Similar limitations apply to other organs.
Humans respond only within a certain range of stimulation. A stimulus must reach an optimal intensity to be noticed. This relationship is studied in psychophysics.
Thresholds and Neural Mechanisms in Sensation
In this section, we have described different types of thresholds as well as neural mechanisms in sensation.
- Absolute Threshold (AL): Minimum intensity needed to activate a sensory system; varies by person and situation, and is defined by detection in 50% of trials.
- Difference Threshold (DL): Smallest difference between two stimuli needed to perceive them as different; also based on 50% of trials.
Sensation also depends on neural mechanisms. The stimulus is encoded as an electrical impulse and sent to the brain. Any defect in the receptor, neural pathway, or brain region can result in partial or complete loss of sensation.
Attentional Process
While our sensory systems receive numerous stimuli at once, we notice only a few. This selection process is called attention. For example, in a classroom filled with people and objects, we may focus only on one or two at a time.
Attention includes:
- Alertness: Readiness to respond (e.g., athletes at the start line).
- Concentration: Focusing on one object while ignoring others.
- Search: Looking for a specific stimulus among many (e.g., finding a sibling in a crowd).
It involves effort allocation, with a focus (clear awareness) and fringe (vague awareness).
Types of Attention
The types of attention are discussed below.
- Selective Attention: Choosing certain stimuli from many.
- External factors: Size, intensity, motion, novelty, human images, rhythmic sounds.
- Internal factors: Motivation (e.g., hunger), cognitive states like interest, attitude, and mental readiness.
- Theories:
- Filter Theory (Broadbent): One stimulus passes through a bottleneck filter.
- Filter-Attenuation Theory (Triesman): Other stimuli are weakened, not blocked.
- Multimode Theory (Johnston & Heinz): Attention operates at sensory, semantic, and conscious levels with increasing mental effort.
- Sustained Attention: Maintaining attention for a long time (vigilance).
- Seen in tasks like air traffic control.
- Influenced by sensory modality, clarity of stimuli, and temporal/spatial certainty.
Perceptual Process
Stimulation of sensory organs leads to sensation. However, sensation alone does not explain what the stimulus means or where it comes from. To understand this, the brain processes the sensory input using learning, memory, motivation, emotions, and other psychological functions.
This process of recognising, interpreting, and giving meaning to sensory input is called perception. It is not just a reflection of the external world but a constructive process influenced by the individual’s personal understanding.
Approaches to Perception
Two of the basic approaches to perception are explained below.
Bottom-up Processing
According to bottom-up processing
- Recognition starts from parts (e.g., features like legs, ears).
- These parts help build the perception of the whole object.
- Emphasises the stimulus.
Top-down Processing
According to top-down processing
- Recognition starts from the whole (e.g., recognising a dog first).
- Leads to the identification of its parts.
- Emphasises the perceiver.
Research shows that both approaches interact to help us make sense of the world around us.
The Perceiver
Humans are not passive recipients of stimuli; they actively interpret the world using their motivations, expectations, cultural knowledge, experiences, beliefs, and attitudes. These factors influence how we assign meaning to what we perceive.
Motivation: Needs and desires affect perception. For example, Hungry individuals perceive ambiguous images as food more often than non-hungry individuals.
Expectations/Perceptual Sets: We tend to perceive what we expect to see, even if it doesn’t match reality. Example: Expecting the milkman at 5:30 A.M., any knock at that time may be perceived as him, even if it’s not
Cognitive Style: Refers to consistent ways individuals process information. It is of two types- field dependent and field independent. Example: The ability to find a hidden triangle quickly
Cultural Background and Experiences: Cultural setting shapes perception
Principles of Perceptual Organisation
Though our visual field contains many separate elements (lines, points, colours), we perceive them as meaningful wholes (e.g., a bicycle, not parts). This process is called form perception.
Gestalt Approach
Below, we have explained the Gestalt approach
- Gestalt psychologists (Köhler, Koffka, Wertheimer) proposed that we perceive stimuli as organised wholes, not separate parts.
- The whole is different from the sum of its parts.
- Our brain tends to organise perception towards “good form” or Pragnanz.
Five-Ground Organisation
We distinguish a figure (focused object) from the ground (background).
Characteristics of Figure vs Ground:
- Figure is more defined; background is formless.
- Figure is more organised.
- Figure has a clear contour.
- Figure appears closer and clearer.
- Background seems distant and less structured.
Gestalt Principles of Organisation
Below, we have discussed the Gestalt Principles of Organisation.
- Proximity: Objects close to each other are seen as a group.
- Similarity: Similar elements (e.g., shape, colour) are grouped together.
- Symmetry: Symmetrical shapes are seen as figures against asymmetrical backgrounds.
- Smallness: Smaller areas are perceived as figures against larger backgrounds.
- Continuity: We group elements that form continuous patterns.
- Surroundedness: Enclosed areas are seen as figures (e.g., black shapes over white).
- Closure: We fill in missing parts to perceive a complete image (e.g., a triangle from incomplete lines).
Perception of Space, Depth, and Distance
Space refers to the visual field in which objects exist and move. Although the images formed on our retinas are two-dimensional, we perceive the world in three dimensions due to the process known as depth or distance perception. This enables us to judge spatial relationships and distances between objects in daily life (e.g., while driving or addressing someone far away).
Cues for Depth Perception
Depth perception depends on two types of cues:
Monocular Cues (Effective with one eye)
These are often used in art and are also known as pictorial cues:
- Relative Size: Smaller retinal images are perceived as farther away.
- Interposition (Overlapping): The object partially covered is perceived as more distant.
- Linear Perspective: Parallel lines appear to converge in the distance (e.g., railway tracks).
- Aerial Perspective: Distant objects appear hazy due to dust and moisture in the air.
- Light and Shade: Highlighted and shadowed areas help indicate depth.
- Relative Height: Larger objects seem closer; smaller objects seem farther.
- Texture Gradient: Denser texture is perceived as more distant.
- Motion Parallax (kinetic cue): Closer objects appear to move faster than distant ones when we are in motion.
Binocular Cues (Require both eyes)
Some of the important terms are:
- Retinal Disparity: Due to the horizontal separation between the eyes (~6.5 cm), each eye sees a slightly different image. Greater disparity indicates a closer object.
- Convergence: Eyes rotate inward to focus on close objects. The degree of convergence indicates distance.
- Accommodation: The ciliary muscles adjust lens thickness based on object distance. Muscle contraction signals a nearby object; relaxation indicates a distant one.
Perceptual Constancies
Despite constant changes in sensory stimulation due to movement or lighting, we tend to perceive objects as stable. This is called perceptual constancy. Common types include:
- Brightness Constancy: Perceived brightness of objects remains stable under varying lighting. (e.g., white paper looks white in sunlight and room light).
- Size Constancy: Perceived size remains constant despite changes in retinal image size due to distance (e.g., a friend approaching doesn’t appear to grow).
- Shape Constancy: Familiar objects retain perceived shape despite changes in viewing angle (e.g., a plate appears circular whether viewed from the front or side).
Illusions
Illusions are misperceptions caused by incorrect interpretation of sensory data, leading to a mismatch between stimulus and perception. They are common and often universal:
- Geometrical Illusions: e.g., Muller-Lyer illusion: lines of equal length appear unequal due to arrowheads.
- Apparent Movement (Phi-Phenomenon): A series of static images shown rapidly (e.g., movies or flashing lights) gives an illusion of motion.
Socio-Cultural Influences on Perception
Perceptual processes vary across cultures due to differing experiences and environments.
- Segall, Campbell, and Herskovits’ Study: African participants were more susceptible to the vertical-horizontal illusion (due to vertical tree exposure), while Westerners were more affected by the Muller-Lyer illusion (due to environments with straight lines and angles).
- Hudson’s African Study: Individuals unfamiliar with pictures struggled with object recognition and depth interpretation, highlighting the role of pictorial experience.
- Sinha and Mishra’s Research: People from varied cultural backgrounds (e.g., forest dwellers, villagers, urban workers) interpreted pictures differently. Familiarity with pictorial materials and cultural learning shapes how actions and events are perceived.
Important Definition in NCERT Notes Class 11 Psychology Chapter 4: Sensory, Attentional, and Perceptual Processes
In this section, you will find the important definitions covered in this chapter.
- Absolute Threshold: Minimum intensity of a stimulus needed to be detected 50% of the time.
- Difference Threshold: Smallest difference between two stimuli noticed 50% of the time.
- Selective Attention: Focusing on certain stimuli while ignoring others.
- Sustained Attention: Maintaining focus on an object or task for a long time.
- Divided Attention: Paying attention to two different tasks or stimuli at the same time.
- Figure-Ground Segregation: Separating a visual image into a main figure and background.
- Filter Theory: Only one stimulus passes through a filter for processing; others are blocked.
- Filter-Attenuation Theory: Unattended stimuli are weakened but still partially processed.
- Bottom-Up Processing: Perception starts with details of a stimulus to build the whole.
- Top-Down Processing: Perception starts with the whole to understand its parts.
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FAQs
Sensation is the basic process of detecting and encoding physical stimuli through sense organs, while perception involves interpreting and giving meaning to those sensations using memory, experience, and other psychological processes.
Monocular cues (like relative size, linear perspective, and interposition) help perceive depth using one eye, whereas binocular cues (like retinal disparity and convergence) require both eyes to judge depth and distance accurately.
Cultural experiences shape perceptual habits; for example, people from forest environments overestimate vertical lines, while those in urban settings are more susceptible to illusions like the Müller-Lyer illusion due to frequent exposure to right angles and enclosed spaces.
