Psych 5.1 Sensation Vs Perception Notes
Sensation and Perception Notes
Learning Objectives
Distinguish between sensation and perception.
Describe the concepts of absolute threshold and difference threshold.
Discuss the roles attention, motivation, and sensory adaptation play in perception.
Sensation
Definition: Sensation occurs when sensory information is detected by sensory receptors.
Sensory Receptors: Specialized neurons that respond to specific types of stimuli (e.g., light causes chemical changes in eye cells).
Transduction: The conversion of sensory stimulus energy into an action potential (nerve impulse) that can be processed by the central nervous system.
Traditional Five Senses: Vision, hearing (audition), smell (olfaction), taste (gustation), and touch (somatosensation).
Other Sensory Systems: The notion of five senses is oversimplified; we also have systems for:
Balance: Vestibular sense.
Body Position and Movement: Proprioception and kinesthesia.
Pain: Nociception.
Temperature: Thermoception.
Absolute Threshold
Definition: The minimum amount of stimulus energy that must be present for the stimulus to be detected 50\% of the time.
Measurement: Determined under highly controlled, optimal conditions for sensitivity.
Examples of Sensitivity:
Most sensitive eye cells can detect a candle flame 30 miles away on a clear night (Okawa & Sampath, 2007).
Hair cells (inner ear receptors) can detect the tick of a clock 20 feet away in quiet conditions (Galanter, 1962).
Physiological Threshold: When a stimulus is strong enough to excite sensory receptors and send nerve impulses to the brain.
Subliminal Messages
Definition: Messages presented below the absolute threshold for conscious awareness; we receive them but are not consciously aware of them.
Speculation: Historically, there has been speculation about their use in advertising, rock music, and self-help programs.
Research Evidence: Studies show people can process and respond to information outside of awareness in laboratory settings (Kunst-Wilson & Zajonc, 1980; Rensink, 2004; Nelson, 2008; Radel et al., 2009; Loersch et al., 2013).
Behavioral Impact: Hidden messages have little effect on behavior outside controlled laboratory environments.
Difference Threshold (Just Noticeable Difference - JND)
Definition: The minimum amount of difference in stimuli required to detect a change between them.
Variability: Unlike the absolute threshold, the difference threshold changes depending on the stimulus intensity.
Example (Cell Phone Brightness):
Dark Movie Theater: A text message illuminating a cell phone screen is easily noticed (large jnd relative to overall low light).
Bright Basketball Arena: The same cell phone brightness goes largely unnoticed (small jnd relative to overall high light).
Weber's Law: Proposed by Ernst Weber in the 1830s. States that the difference threshold is a constant fraction of the original stimulus, meaning the jnd increases as the intensity of the original stimulus increases.
Perception
Definition: The way sensory information is organized, interpreted, and consciously experienced.
Relationship with Sensation: Our sensory receptors constantly collect information (sensation), but how we interpret it (perception) determines our interaction with the world.
Physical vs. Psychological: Sensation is a physical process, while perception is a psychological process.
Example: Smelling cinnamon rolls (sensation) vs. perceiving "Mmm, this smells like Grandma's holiday bread" (perception).
Processing Types
Bottom-Up Processing: Sensory information from a stimulus in the environment drives the process.
Example: The sudden sound of breaking glass in a noisy restaurant capturing your attention automatically.
Top-Down Processing: Knowledge and expectancy drive the process. Generally goal-directed, slow, deliberate, effortful, and under conscious control.
Example: Searching for misplaced yellow keys; you use your knowledge (keys are not on ceiling fans) and expectations (look for yellowness of a certain size in specific locations like counters).
Factors Affecting Perception
Sensory Adaptation
Definition: Failure to perceive stimuli that remain relatively constant over prolonged periods of time because sensory receptors become less sensitive.
Example: A bright, flashing road construction light outside a hotel room becomes unnoticeable after a short period of watching television, even though the light is still flashing and sensed by photoreceptors.
Distinction: Demonstrates that sensation and perception are distinct processes, as the sensation of light is still present, but the perception of its flashing is not.
Attention
Role: Plays a significant role in determining what is sensed versus what is perceived.
Example (Party Background Noise): Engaging in an interesting conversation at a party might lead you to tune out background music; you wouldn't be able to recall the song that just played because you weren't attending to it.
Inattentional Blindness: Failure to notice something that is completely visible because attention is actively focused on something else (Mack & Rock, 1998; Simons & Chabris, 1999).
Simons and Chabris (1999) Gorilla Study: Participants watching a video and counting basketball passes by a white-shirted team failed to notice a person in a black gorilla costume walking through the scene for 9 seconds. Nearly half the participants did not notice.
Most et al. (2000) Red Cross Experiment: Participants focusing on black or white objects moving across a screen did not notice a red cross passing across it (about one-third of subjects).
Motivation
Role: Can affect our ability to discriminate between a true sensory stimulus and background noise.
Example: Thinking you hear the phone ring while taking a shower because you are expecting an important call.
Signal Detection Theory: The ability to identify a stimulus when it is embedded in a distracting background.
Example: A mother being awakened by her baby's quiet murmur but not other sounds while asleep.
Practical Application: Improving air traffic controller accuracy in detecting planes (blips) among many signals on radar screens (Swets, 1964).
Beliefs, Values, Prejudices, Expectations, and Life Experiences
General Impact: Our cognitive and cultural background significantly shapes our perceptions.
Depth Perception (Developmental): Individuals deprived of binocular vision during critical developmental periods have difficulty perceiving depth (Fawcett, Wang, & Birch, 2005).
Cultural Context: Shared experiences within a culture can profoundly affect perception (Segall, Campbell, & Herskovits, 1963).
Müller-Lyer Illusion (Figure 5.4): Lines appear to be different lengths but are actually identical. Westerners are more prone to this visual illusion.
Explanation: People in Western cultures live in a