Introduction
This chapter explores how we gather information from our environment through sensory processes, select relevant information through attention, and interpret this information through perception. These three interrelated processes form the basis of our understanding of the world.
Quote: "The quality of life is determined by its activities." — Aristotle
Knowing the World
Our knowledge of the world depends on three basic processes:
- Sensation: Detection and encoding of physical stimuli by sense organs
- Attention: Selection of relevant stimuli from the environment
- Perception: Interpretation and meaningful organization of sensory information
Nature and Varieties of Stimulus
Our environment contains various types of stimuli that can be detected by specialized sense organs:
- Five external senses: Vision (eyes), hearing (ears), smell (nose), taste (tongue), touch (skin)
- Two internal senses: Kinesthetic (body position) and vestibular (balance) systems
Sense Modalities
Sensation is the initial experience of a stimulus registered by a sense organ. Each sense organ is specialized for dealing with particular information, forming different sense modalities.
Functional Limitations of Sense Organs
Our senses have thresholds that limit what we can perceive:
- Absolute threshold (AL): Minimum stimulus value required to activate a sensory system (e.g., minimum sugar granules needed to taste sweetness)
- Difference threshold (DL): Smallest difference between two stimuli needed to notice them as different
Attentional Processes
Attention is the process of selecting certain stimuli while filtering out others. Key properties of attention include:
- Alertness: Readiness to deal with stimuli
- Concentration: Focusing awareness on specific objects
- Search: Looking for specific objects among many
Types of Attention
Attention can be divided into several types:
Selective Attention
Selection of a limited number of stimuli from many. Influenced by:
- External factors: Size, intensity, motion, novelty of stimuli
- Internal factors: Motivational and cognitive factors (needs, interests, attitudes)
Theories of Selective Attention
Filter Theory (Broadbent): Stimuli create a bottleneck; only one passes through a selective filter
Filter-Attenuation Theory (Triesman): Unselected stimuli are weakened but not completely blocked
Multimode Theory (Johnston & Heinz): Flexible selection at three processing stages
Sustained Attention
Ability to maintain focus on an object or event for longer durations (also called vigilance). Influenced by:
- Sensory modality (auditory better than visual)
- Clarity of stimuli
- Temporal and spatial uncertainty
Divided Attention
Attending to multiple tasks simultaneously is possible with highly practiced activities that become automatic. Automatic processing:
- Occurs without intention
- Takes place unconsciously
- Involves little thought
Span of Attention
The "magic number" of 7±2 describes how many objects we can attend to briefly. This is why phone numbers and license plates are designed with this limit in mind.
Attention Deficit Hyperactivity Disorder (ADHD)
A behavioral disorder characterized by:
- Impulsivity and excessive motor activity
- Difficulty in sustaining attention
- More common in boys
Treatment options include medication (e.g., Ritalin) and behavioral management programs.
Perceptual Processes
Perception involves interpreting sensory information to construct meaningful understanding. Sub-processes include:
- Stimulus detection by sensory receptors
- Attention to relevant stimuli
- Processing in the central nervous system
- Interpretation using memory, motivation, and other psychological factors
Processing Approaches in Perception
- Bottom-up processing: Recognition begins with parts leading to whole
- Top-down processing: Recognition begins with whole leading to parts
The Perceiver
Factors influencing perception:
- Motivation: Needs and desires affect interpretation
- Expectations/Perceptual Sets: We often see what we expect to see
- Cognitive Styles: Field-dependent (holistic) vs. field-independent (analytic) approaches
- Cultural Background: Different experiences lead to different interpretations
Principles of Perceptual Organization (Gestalt Psychology)
We perceive organized wholes rather than discrete parts. Key principles:
| Principle | Description | Example |
|---|---|---|
| Figure-Ground Segregation | Separating figures from background | Seeing faces or vase in Rubin's figure |
| Proximity | Close objects perceived as belonging together | Columns of dots rather than square pattern |
| Similarity | Similar objects perceived as groups | Alternating columns of circles and squares |
| Continuity | Preference for continuous patterns | Seeing crossing lines rather than four lines meeting |
| Closure | Tendency to complete incomplete figures | Seeing a triangle from angled lines |
| Smallness | Smaller areas seen as figures | Black cross rather than white cross in circle |
| Symmetry | Symmetrical areas seen as figures | Black symmetrical shapes against white background |
Perception of Space, Depth, and Distance
We perceive 3D space using various cues:
Monocular Cues (Psychological Cues)
Depth perception with one eye:
- Relative Size: Smaller retinal image = farther object
- Interposition: Overlapped object appears farther
- Linear Perspective: Parallel lines appear to converge
- Aerial Perspective: Distant objects appear hazy
- Light and Shade: Highlights and shadows indicate depth
- Texture Gradient: Increased density = greater distance
- Motion Parallax: Close objects move faster than distant ones
Binocular Cues (Physiological Cues)
Depth perception requiring both eyes:
- Retinal Disparity: Different images from each eye
- Convergence: Eyes turn inward for near objects
- Accommodation: Lens thickness changes for focus
Perceptual Constancies
We perceive objects as relatively stable despite changes in sensory input:
- Size Constancy: Object size remains constant despite distance changes
- Shape Constancy: Shape remains constant despite orientation changes
- Brightness Constancy: Brightness remains constant despite illumination changes
Illusions
Misperceptions resulting from misinterpretation of sensory information:
Müller-Lyer Illusion
Lines appear unequal due to arrowhead differences
Vertical-Horizontal Illusion
Vertical line appears longer than equal horizontal line
Other types of illusions include:
- Apparent Movement (Phi Phenomenon): Stationary images perceived as moving (e.g., cinema)
- Geometrical Illusions: Universal misperceptions of shapes and sizes
Socio-Cultural Influences on Perception
Cultural experiences shape perception:
- African subjects more susceptible to horizontal-vertical illusion
- Westerners more susceptible to Müller-Lyer illusion
- People unfamiliar with pictures have difficulty interpreting depth cues
Key Terms
Absolute threshold: Minimum stimulus value needed for detection
Binocular cues: Depth cues requiring both eyes
Bottom-up processing: Perception starting from sensory input
Depth perception: Seeing the world in three dimensions
Difference threshold: Smallest noticeable difference between stimuli
Divided attention: Attending to multiple tasks simultaneously
Figure-ground segregation: Separating objects from background
Gestalt: Organized whole different from sum of parts
Monocular cues: Depth cues available to one eye
Perceptual constancies: Stable perceptions despite changing input
Phi-phenomenon: Apparent movement illusion
Selective attention: Focusing on specific stimuli
Sustained attention: Maintaining focus over time
Top-down processing: Perception guided by knowledge and expectations
Summary
- We know our world through sensation, attention, and perception processes
- Our senses have thresholds (absolute and difference) that limit what we can perceive
- Attention involves selection (selective), maintenance (sustained), and division (divided) of focus
- Perception involves organizing sensory input into meaningful wholes (Gestalt principles)
- Depth perception uses monocular (one-eye) and binocular (two-eye) cues
- Perceptual constancies maintain stable perceptions despite changing input
- Illusions demonstrate how perception can differ from reality
- Cultural background significantly influences perceptual experiences
Review Questions
- What are the functional limitations of our sense organs?
- Define attention and explain its different properties.
- How does selective attention differ from sustained attention?
- What are the main principles of Gestalt psychology regarding perception?
- Explain how we perceive depth in our environment.
- What are perceptual constancies and why are they important?
- Why do visual illusions occur?
- How does culture influence our perceptual experiences?
Project Ideas
- Analyze advertisements to identify attentional and perceptual strategies used
- Compare descriptions of objects by sighted and visually impaired individuals
- Investigate cultural differences in perception using optical illusions