Ch02: Sensation, Perception & Attention（感觉、知觉与注意）

Preparatory Mindset

Psychology's most fundamental processes — sensation (raw input), perception (interpretation), and attention (selection). The exam tests: 5 external senses (sight, hearing, smell, taste, touch), sensory threshold (absolute & difference), constancy, illusions, and types of attention (selective, divided, sustained, executive). The 知觉 video (with the passing-balls-and-gorilla test) anchors inattentional blindness.

Exam mindset: know the difference between sensation (bottom-up, raw input from receptors) and perception (top-down, interpretation by the brain); the just-noticeable difference (JND / difference threshold); and inattentional blindness (the famous gorilla experiment).

Core Concepts

1. Sensory process — definition (MUST KNOW)

• The process that organizes and distinguishes sensation from one's own body and the environment — making it possible to use the body effectively within the environment
• Two stages: sensation (detection) → perception (interpretation)

2. External sensations (MUST KNOW)

• External sensations vision, hearing, smell, taste, touch (and additional: vestibular, proprioception)
• Internal sensations: proprioception (body position), kinesthesia, visceral sensations

3. Sensitivity & sensory thresholds (MUST KNOW)

• Sensitivity: the quality or condition of being sensitive — the capacity of an organism to respond to stimulation
• Absolute threshold: the weakest stimulus that an organism can sense (detect 50% of the time)
• Difference threshold (JND — just-noticeable difference): the smallest difference between stimuli that a person can detect — Weber's Law: ΔI/I = k (constant proportion)
• Sense of contrast: ability to perceive sharp and clear outlines of very small objects; identify small differences in shading/patterns

4. Sensory deprivation (perceptual isolation)

• The removal of stimuli from one or more of the senses
• Prolonged deprivation → cognitive/perceptual disturbances; used in research (e.g., Ganzfeld experiments) and occasionally in clinical settings

5. Perception (MUST KNOW)

• The ability to see, hear, or become aware of something through the senses
• Bottom-up (data-driven) + top-down (knowledge/expectation-driven) processing
• Constancy: the tendency to perceive a familiar item as having a standard shape, size, and brightness regardless of changes in the stimulus (e.g., door looks rectangular even at an angle)
• Illusions: special perceptual experiences in which information arising from real external stimuli leads to an incorrect perception or false impression (Müller-Lyer, size-weight, Ponzo)
• Perceptual organization: Gestalt principles — proximity, similarity, closure, continuity, figure-ground

6. Attention (MUST KNOW — 4 types)

1. Selective attention — attending to one stimulus while others are present (cocktail party effect) 2. Divided attention — attending to multiple stimuli simultaneously (multitasking) 3. Sustained attention (vigilance) — attending to a specific stimulus over a long period 4. Executive attention — attending to what really matters by blocking out unimportant features (frontal lobe, top-down control)

• Attention: the concentration of awareness on some phenomenon to the exclusion of other stimuli
• Four types:
• Inattentional blindness (MUST KNOW): occurs when an individual fails to recognize an unexpected stimulus in plain sight, due to lack of attention — not vision defects. Famous example: the gorilla experiment (passing balls — many people miss the gorilla walking through).
• Change blindness: related — missing visual changes when attention is diverted (flicker paradigm)

7. Clinical relevance

• Visual perception disorders: agnosia (object recognition), prosopagnosia (face blindness), alexia (word blindness)
• Attention disorders: ADHD (hypersensitive/distractible; inattention/impulsivity), hemispatial neglect (parietal lobe lesion)
• Auditory: neglect of one side with strokes
• Illusions in clinical practice: Charles Bonnet syndrome (visual hallucinations in macular degeneration — patients often lack insight)

High-Yield Points

• Absolute threshold = weakest detectable stimulus; Difference threshold = JND (Weber's law: ΔI/I = k)
• Sensation (raw input) → Perception (interpretation); bottom-up + top-down
• Constancy = stable perception despite stimulus change (size/shape/brightness)
• Illusion = incorrect perception from real stimulus (Müller-Lyer, Ponzo)
• 4 types of attention: selective, divided, sustained, executive
• Inattentional blindness = missing the unexpected (the gorilla passes unnoticed)
• 5 external senses: sight, hearing, smell, taste, touch
• Sensory deprivation → cognitive/perceptual disturbances
• Gestalt principles: proximity, similarity, closure, continuity, figure-ground

Topic Summary

The sensory process organizes and distinguishes sensation from body and environment, letting the body function effectively. External sensations include sight, hearing, smell, taste, touch. Sensitivity is the capacity to respond to stimuli; absolute threshold is the weakest detectable stimulus; difference threshold (JND/Weber's law) is the smallest detectable difference. Sensory deprivation removes stimuli from senses. Perception interprets sensation through bottom-up and top-down processing; constancy maintains stable perception despite changes; illusions are false perceptions from real stimuli (e.g., Müller-Lyer). Attention is the concentration of awareness, with four types: selective (focus on one), divided (multitask), sustained (vigilance), and executive (top-down). Inattentional blindness (the gorilla experiment) shows that focused attention can miss the unexpected. Clinical correlates: agnosia, prosopagnosia, ADHD, hemispatial neglect.