Chapter Notes

Introduction

This chapter explores how we gather information about the world around us and inside our bodies. We have sensory receptors, like our eyes and ears, that collect information. However, we don't process everything at once. We use attention to notice and register specific information. Finally, we'll look at perception, which is the process that allows us to make sense of this information and understand the world in a meaningful way. We will also see how our senses can sometimes be tricked by certain images or figures.

Knowing the World

Our understanding of the world—from the chair you're sitting on to the trees outside—comes from our sense organs. These organs, like our eyes and ears, collect information from both the external environment and our own bodies. This information is the foundation of all our knowledge.

However, simply collecting information isn't enough. For us to know something, three basic processes must occur:

1. Sensation: Our sense organs must first register information about an object's qualities (like its size, shape, and color).
2. Attention: The object must draw our attention to be registered.
3. Perception: The registered information is sent to the brain, which gives it meaning.

These three processes are so closely linked that they are often considered parts of a single larger process called cognition.

Nature and Varieties of Stimulus

Our environment is filled with a wide variety of stimuli—things we can see, hear, smell, taste, or touch. To handle these different stimuli, humans have a set of seven highly specialized sense organs, also known as sensory receptors.

• Five External Sense Organs: These collect information from the outside world.
  • Eyes for vision.
  • Ears for hearing.
  • Nose for smell.
  • Tongue for taste.
  • Skin for touch, warmth, cold, and pain.
• Two Deep Senses: These provide information about our own body.
  • Kinesthetic system: Informs us about our body position and the movement of our body parts.
  • Vestibular system: Also provides information about body position and movement.

With these seven sense organs, we can register many different qualities of stimuli, such as whether a light is bright or dim, or if a sound is loud or faint.

Sense Modalities

The initial experience of a stimulus that is registered by a sense organ is called sensation. It's the process of detecting and encoding physical stimuli from the world. Sensation refers to the immediate, basic experiences like "hard," "warm," or "blue."

Because each sense organ is specialized to deal with a particular kind of information (like eyes for light or ears for sound), each one is known as a sense modality.

Functional Limitations of Sense Organs

Our senses can't detect everything. They operate within a limited range. For example, our eyes cannot see light that is extremely dim or extremely bright, and our ears can't hear sounds that are too faint or too loud. The study of the relationship between stimuli and the sensations they produce is called psychophysics.

For a stimulus to be noticed, it must have a minimum intensity.

• Absolute Threshold (AL): This is the minimum value of a stimulus needed to activate a sensory system. The AL is not a fixed point; it varies between people and situations. Therefore, it's defined as the minimum value that a person can detect 50 percent of the time.

• Difference Threshold (DL): This is the smallest difference in the value of two stimuli that is necessary for a person to notice them as different. Like the AL, it's the point where a difference is detected 50 percent of the time.

For sensation to occur, a stimulus must not only be strong enough to be detected, but the sense organ must also be functioning correctly. Any damage to the receptor, its neural pathway, or the related brain area can lead to a partial or complete loss of sensation.

Attentional Processes

While our senses are constantly bombarded with stimuli, we only notice a select few at any given time. The process of selecting certain stimuli from a larger group is called attention.

Attention involves more than just selection. It also includes other properties:

• Alertness: An individual's readiness to deal with stimuli. A runner at the starting line is in a state of alertness, waiting for the whistle.
• Concentration: Focusing awareness on specific objects while ignoring others. A student concentrating on a lecture ignores other noises in the school.
• Search: Looking for a specific object among many. When you pick up a sibling from school, you search for their face in a crowd of children.

Attention has a focus (the object or event at the center of our awareness) and a fringe (objects or events we are only vaguely aware of).

Attention can be divided into a few main types, including selective, sustained, and divided attention.

Selective Attention

Selective attention is the process of selecting a limited number of stimuli from a larger pool. Our perceptual system has a limited capacity, meaning it can only process a few stimuli at a time. The key question is: which stimuli get selected?

Factors Affecting Selective Attention

The factors that determine what we pay attention to can be divided into two categories:

• External Factors (related to the stimuli):
  • Size, intensity, and motion: Large, bright, and moving stimuli are more likely to catch our attention.
  • Novelty and complexity: New and moderately complex stimuli are attention-grabbing.
  • Sudden and intense stimuli: A loud bang or a sudden flash of light has a powerful ability to draw our attention.
• Internal Factors (related to the individual):
  • Motivational Factors: These are related to our biological or social needs. When you're hungry, you're more likely to notice the smell of food.
  • Cognitive Factors: These include your interest, attitude, and preparatory set. We pay more attention to things that interest us or that we have a favorable attitude towards. A preparatory set creates a mental readiness to respond to certain stimuli over others.

Theories of Selective Attention

Psychologists have proposed several theories to explain how selective attention works.

1. Filter Theory (Broadbent, 1956): This theory suggests that many stimuli enter our sensory receptors at once, creating a "bottleneck." They pass through a short-term memory system and then to a selective filter, which allows only one stimulus to pass through for higher-level processing. All other stimuli are blocked out.
2. Filter-attenuation Theory (Triesman, 1962): Triesman modified Broadbent's theory, proposing that the filter doesn't completely block other stimuli but only attenuates (weakens) them. This explains why some personally relevant stimuli, like hearing your name in a noisy room, can still "slip through" the filter and be noticed.
3. Multimode Theory (Johnston and Heinz, 1978): This theory views attention as a flexible system. It proposes that selection can happen at three different stages:
   • Stage 1: Based on sensory features (e.g., visual images).
   • Stage 2: Based on semantic meaning (e.g., the names of objects).
   • Stage 3: When sensory and semantic representations enter consciousness. According to this theory, more processing requires more mental effort. Selecting a message early (Stage 1) is easier than selecting it late (Stage 3).

Divided Attention

Sometimes, we can attend to more than one thing at the same time, which is known as divided attention.

Automatic processing has three key features:

• It occurs without intention.
• It happens unconsciously.
• It involves little to no thought (like tying your shoelaces).

Sustained Attention

While selective attention is about choosing what to focus on, sustained attention is about maintaining that focus over a long period. This is also called vigilance.

Factors Influencing Sustained Attention

Several factors affect our ability to maintain vigilance:

• Sensory Modality: Performance is often better with auditory (hearing) stimuli than with visual stimuli.
• Clarity of Stimuli: Intense and long-lasting signals make it easier to maintain attention.
• Temporal Uncertainty: We are better at attending to stimuli that appear at regular intervals rather than irregular ones.
• Spatial Uncertainty: It is easier to attend to stimuli that appear in a fixed location compared to those that appear in random locations.

Span of Attention

Our attention has a limited capacity. The number of objects a person can attend to in a brief exposure (a fraction of a second) is called the span of attention or perceptual span.

Attention Deficit Hyperactivity Disorder (ADHD)

ADHD is a common behavioral disorder in children, characterized by impulsivity, excessive motor activity, and an inability to attend. It is more common in boys than girls. The core feature is difficulty in sustaining attention, which leads to problems like distractibility, not following instructions, and poor performance in school despite normal intelligence.

• Causes: The causes are thought to be multiple. While a biological basis is not strongly supported, links to dietary factors (like food coloring) and social-psychological factors (like home environment) have been found.
• Treatment: A drug called Ritalin is often used to decrease over-activity and increase concentration, but it can have side effects. Behavioral management programs that use positive reinforcement and cognitive behavioral training (teaching children to "stop, think, and then do") have also been successful.

Perceptual Processes

Sensation provides raw data (a flash of light, a sound), but it doesn't give us an understanding of that data (the source of the light or sound). The process by which we recognize, interpret, and give meaning to sensory information is called perception.

Perception is not just about interpreting the world as it is; it is also a process of construction. We use our learning, memory, motivation, and emotions to build our understanding of stimuli from our own point of view.

Processing Approaches in Perception

How do we recognize an object? Do we see its parts first and then the whole, or the whole first and then its parts?

• Bottom-up Processing: This approach suggests that recognition begins with the individual parts or features of a stimulus. These parts are then pieced together to recognize the whole object. This approach emphasizes the stimulus itself.
• Top-down Processing: This approach suggests that recognition begins with the whole object, which then allows us to identify its parts. This approach emphasizes the role of the perceiver's knowledge, expectations, and experiences.

In reality, both processes interact to help us understand the world.

The Perceiver

We are not passive receivers of information. Our personal characteristics play a huge role in how we perceive the world.

• Motivation: Our needs and desires strongly influence what we perceive. For example, hungry people are more likely to see ambiguous images as pictures of food.
• Expectations or Perceptual Sets: We have a strong tendency to see what we expect to see. If your milkman always arrives at 5:30 A.M., you might perceive any knock on the door at that time as being the milkman, even if it's someone else.
• Cognitive Styles: This refers to a consistent way of dealing with the environment. One well-studied style is field dependent vs. field independent.
  • Field dependent people tend to perceive the world globally or holistically.
  • Field independent people tend to perceive the world by breaking it down into smaller, analytic parts. They are better at finding hidden figures within a larger design.
• Cultural Background and Experiences: The culture we grow up in shapes our perception. People from environments without pictures may struggle to recognize objects in them or interpret depth. Similarly, Eskimos can distinguish between many types of snow that others cannot see as different.

Principles of Perceptual Organisation

Our visual world is made of points, lines, and colors, but we perceive them as organized, whole objects—a process known as form perception.

The Gestalt psychologists, including Köhler, Koffka, and Wertheimer, provided the most widely accepted explanation for this. "Gestalt" is a German word meaning a regular figure or form. They argued that we perceive stimuli as an organized "whole," not as a collection of separate parts.

Figure-Ground Segregation

The most basic form of perceptual organization is separating a figure from its background. When we look at a scene, some objects (the figure) seem to stand out, while everything else recedes into the background.

Characteristics that distinguish a figure from the ground:

• The figure has a definite form, while the ground is formless.
• The figure is more organized and has a clear outline (contour).
• The figure appears to stand out and be closer, while the ground stays behind.

Gestalt Principles of Organisation

Gestalt psychologists identified several principles that explain how we group stimuli into meaningful wholes.

• The Principle of Proximity: Objects that are close to each other in space or time are perceived as belonging together. We see columns of dots, not just a square of dots.
• The Principle of Similarity: Objects that are similar to one another are perceived as a group. We see columns of circles and columns of squares, not rows of mixed shapes.
• The Principle of Continuity: We tend to perceive objects as forming a continuous pattern. We see two crossing lines rather than four separate lines meeting at the center.
• The Principle of Smallness: Smaller areas tend to be seen as figures against a larger background.
• The Principle of Symmetry: Symmetrical areas are more likely to be seen as figures.
• The Principle of Surroundedness: An area that is surrounded by another tends to be perceived as the figure.
• The Principle of Closure: We tend to mentally fill in gaps in stimuli to perceive a complete, whole object. We see a triangle even if its sides are not fully drawn.

Perception of Space, Depth, and Distance

The world we live in is three-dimensional. Even though the images projected onto our retinas are two-dimensional, we perceive the world in 3D. The process of viewing the world in three dimensions is called depth perception. This ability is crucial for everyday tasks like driving or judging how far away a person is.

To perceive depth, we rely on two types of information, or cues.

Monocular Cues (Psychological Cues)

Monocular cues are depth cues that are effective with just one eye. Artists use these "pictorial cues" to create the illusion of depth in 2D paintings.

• Relative Size: When we see two objects we know are similar in size, the one that appears smaller is perceived as being farther away.
• Interposition or Overlapping: If one object partially blocks another, the one being blocked is perceived as farther away.
• Linear Perspective: Parallel lines, like railway tracks, appear to converge (come together) as they get farther away. The more they converge, the farther they seem.
• Aerial Perspective: Distant objects often look hazy or blurry because of microscopic particles in the air.
• Light and Shade: Shadows and highlights on an object can give us clues about its distance and depth.
• Relative Height: In our visual field, larger objects are perceived as closer, and smaller objects as farther away.
• Texture Gradient: Surfaces with a dense texture are seen as farther away. As a textured surface (like a field of stones) recedes, its texture appears finer and more dense.
• Motion Parallax: This is a kinetic (movement-based) cue. When you are moving, closer objects appear to move "against" your direction of travel, while distant objects seem to move "with" you.

Binocular Cues (Physiological Cues)

Binocular cues are depth cues that require the use of both eyes.

• Retinal or Binocular Disparity: Because our two eyes are in slightly different locations (about 6.5 cm apart), each eye receives a slightly different image of the same object. The brain uses the difference, or disparity, between these two images to judge distance. A large disparity means the object is close; a small disparity means it's far away.
• Convergence: To look at a nearby object, our eyes turn inward, or converge. Muscles send signals to the brain about how much the eyes are turning. The more they converge, the closer the object is perceived to be.
• Accommodation: The lens of our eye changes shape to focus on objects at different distances, a process called accommodation. Ciliary muscles contract to focus on near objects and relax for far objects. The brain uses signals about this muscle activity as a cue for distance.

Perceptual Constancies

Even though the sensory information we receive is constantly changing as we move, our perception of objects remains remarkably stable. This is called perceptual constancy.

• Size Constancy: We perceive an object as being the same size, regardless of its distance from us (which changes the size of its image on our retina). Your friend doesn't appear to shrink as they walk away from you.
• Shape Constancy: We perceive familiar objects as having a constant shape, even when our viewing angle changes the shape of the retinal image. A dinner plate is seen as circular even when viewed from the side, where its retinal image is an ellipse.
• Brightness Constancy: We perceive an object as having a constant brightness, even when the amount of light it reflects changes. A piece of white paper looks white in both bright sunlight and dim room light.

Illusions

Our perceptions are not always accurate. Illusions are misperceptions that result from misinterpreting sensory information. They are a mismatch between a physical stimulus and our perception of it.

• Universal illusions (or permanent illusions) are experienced by almost everyone in the same way and do not change with practice (e.g., railway tracks appearing to converge).
• Personal illusions vary from person to person.

Geometrical Illusions

These are illusions involving geometric shapes and lines.

• Muller-Lyer Illusion: Two lines of equal length appear to be different lengths because of the direction of the arrowheads at their ends. The line with outward-pointing fins appears longer.
• Vertical-Horizontal Illusion: A vertical line appears longer than a horizontal line of the same length.

Apparent Movement Illusion

This illusion occurs when motionless images, presented one after another at a certain speed, create the perception of movement. This is called the phi-phenomenon.

Socio-Cultural Influences on Perception

Does everyone perceive the world in the same way? Studies show that our cultural background and experiences significantly influence our perception.

• Illusion Susceptibility: Studies comparing people from different cultures found that their susceptibility to certain illusions varies. For example, African subjects living in dense forests were more susceptible to the vertical-horizontal illusion (perhaps due to regularly seeing tall trees), while Western subjects living in "carpentered worlds" with many right angles were more susceptible to the Muller-Lyer illusion. This suggests that perceptual habits are learned within a cultural context.
• Pictorial Perception: People from cultures with little exposure to pictures have difficulty recognizing objects and interpreting depth cues in 2D images. Studies have shown that cultural experience is crucial for understanding the actions and events depicted in pictures.

These findings show that perception is not a universal, fixed process. Instead, people actively construct their understanding of the world based on their unique personal, social, and cultural conditions.