AP Psychology 1.5-1.6: Sleep and Sensation

Melatonin

A hormone released by the pineal gland during sleep or darkness that helps regulate biological rhythms and may influence immune function.

Sleep

A state characterized by low physical activity and reduced sensory awareness, regulated by both circadian timing and homeostatic mechanisms.

What is sleep rebound, and what does it demonstrate about sleep regulation?

Sleep rebound is the tendency to fall asleep more quickly after sleep deprivation. It demonstrates homeostatic regulation: the need for sleep increases when sleep is lost.

How can electroencephalography (EEG) be used to study sleep?

EEG records patterns of electrical activity in the brain. Different sleep phases can be distinguished by their characteristic EEG activity.

Which brain regions are especially involved in regulating sleep and wakefulness?

The thalamus, hypothalamus, and pons work together to regulate sleep. The hypothalamus contains the suprachiasmatic nucleus (SCN), and the pons is particularly important for REM sleep.

Suprachiasmatic nucleus (SCN)

A nucleus in the hypothalamus that functions as the body's biological clock and helps regulate circadian rhythms.

What roles do the hypothalamus and thalamus play in sleep?

The hypothalamus contains the SCN and other nuclei involved in regulating slow-wave sleep. These nuclei work with the thalamus to coordinate sleep-related brain activity.

What role does the pons play in sleep?

The pons contributes importantly to the regulation of rapid eye movement (REM) sleep.

Which gland secretes melatonin, and what is one major function of this hormone?

The pineal gland secretes melatonin. Melatonin helps regulate biological rhythms, including the sleep-wake cycle.

What sleep-associated hormones are secreted by the pituitary gland?

The pituitary gland secretes follicle-stimulating hormone (FSH), luteinizing hormone (LH), and growth hormone during sleep.

What roles do FSH and LH play in relation to sleep-associated hormone secretion?

FSH and LH are pituitary hormones released during sleep that help regulate reproductive-system functions.

Growth hormone during sleep

Growth hormone released by the pituitary during sleep supports physical growth and maturation and contributes to metabolic processes.

What is the adaptive or evolutionary theory of sleep?

This theory proposes that sleep evolved because it improves survival or reproductive success. Proposed benefits include conserving energy and reducing exposure to predators, although evidence for these explanations is mixed.

Why is energy conservation an incomplete explanation for why humans sleep?

Although sleep reduces energy expenditure, ordinary rest and inactivity might also conserve energy. Comparative research has even found that species with greater energetic demands may not sleep longer.

What does the predation-risk hypothesis propose about sleep?

It proposes that sleeping in protected locations, especially during darkness, reduces the risk of being harmed by predators. Cross-species evidence is complex and does not show a simple relationship between predation risk and sleep duration.

Why might sleep have different adaptive functions in different species?

Species face different ecological pressures, including varying food availability, activity patterns, and predation risks. Therefore, evolution may produce different sleep durations and patterns rather than one universal adaptive function.

What evidence supports a cognitive function for sleep?

Sleep deprivation impairs attention, decision-making, cognition, and long-term memory. Sleep, especially slow-wave sleep after learning, can improve task performance and support memory formation.

Why can staying awake all night to study be counterproductive?

Sleep loss disrupts attention, decision-making, and memory formation. Because sleep helps consolidate learning, sacrificing sleep may reduce performance despite adding study time.

What cognitive abilities may benefit from adequate sleep besides memory?

Adequate sleep has been associated with improved creative thinking, language learning, inferential judgments, and processing of emotional information.

Sensation

The detection of physical stimulus energy by specialized sensory receptors.

Perception

The organization, interpretation, and conscious experience of sensory information.

How do sensation and perception differ?

Sensation is primarily the physical detection of stimulus energy by receptors, whereas perception is the psychological interpretation of that information. A stimulus can be sensed without reaching conscious perception.

Transduction

The conversion of stimulus energy into neural signals, such as action potentials, that can be processed by the nervous system.

What sensory systems exist beyond vision, hearing, smell, taste, and touch?

Additional systems include the vestibular sense for balance, proprioception and kinesthesia for body position and movement, nociception for pain, and thermoception for temperature.

Absolute threshold

The minimum stimulus energy that can be detected 50% of the time under specified conditions.

Why is the absolute threshold defined using detection on 50% of trials?

Detection depends on both stimulus intensity and conditions such as background noise and attention. The 50% criterion provides a standardized point for comparing sensory sensitivity.

Subliminal stimulus

A stimulus presented below the absolute threshold for conscious awareness. Such information may sometimes be processed, but evidence indicates that subliminal messages generally have little effect on behavior outside controlled laboratory conditions.

Difference threshold (just noticeable difference, or JND)

The smallest change in stimulus intensity that can be detected reliably as a difference.

Weber's law

The difference threshold is a constant fraction of the original stimulus intensity: $\Delta I / I = k$, where $I$ is the starting intensity, $\Delta I$ is the detectable change, and $k$ is a constant for that sensory system.

How does Weber's law explain why the same change may be noticeable in one setting but not another?

Detectability depends on the ratio of the change to the original intensity, not simply on the absolute size of the change. A phone screen may be noticeable in a dark theater but not in a brightly lit arena.

Bottom-up processing

Perceptual processing driven by sensory information entering from the environment. An unexpected loud crash capturing attention is an example.

Top-down processing

Perceptual processing guided by prior knowledge, expectations, goals, and experience. Searching likely locations for a misplaced object uses top-down processing.

How do bottom-up and top-down processing work together?

Bottom-up processing supplies information from the stimulus, while top-down processing uses knowledge and expectations to interpret or guide attention toward that information.

Signal detection theory

A framework for explaining how people detect meaningful signals within distracting background information. Detection depends not only on stimulus strength but also on attention, expectations, motivation, and the consequences of responding.

How can motivation alter sensory detection?

Motivation increases readiness to detect stimuli that are important to a person. Someone expecting an urgent phone call may mistake background noise for a ringtone, while a parent may detect a child's quiet sound during sleep.

How can expectations and prior experience influence perception?

Beliefs, values, prejudices, expectations, and past experiences influence how sensory information is organized and interpreted. Consequently, people may perceive the same stimulus differently.

Sensory adaptation

A reduced conscious response to an unchanging or repetitive stimulus, even though sensory receptors may continue responding. For example, a person may stop noticing a continuously flashing light after prolonged exposure.

Why can a person sense a stimulus without perceiving it?

Sensory receptors may continue detecting the stimulus, but adaptation, limited attention, or competing information can prevent it from entering conscious awareness.

Inattentional blindness

Failure to notice a visible stimulus because attention is focused on another task or object. Focusing on counting basketball passes can cause observers to miss an unexpected person in the scene.

What does inattentional blindness reveal about attention?

Conscious perception is selective rather than a complete record of everything sensed. Focusing attention on one goal can prevent awareness of other clearly visible events.

How can culture influence visual perception?

Regular exposure to different environments can shape perceptual expectations. For example, people accustomed to built environments with many straight lines may be more susceptible to the Müller-Lyer illusion.

Müller-Lyer illusion

A visual illusion in which identical line segments appear to have different lengths because of the orientation of arrow-like endpoints or surrounding visual context.

Why do identical lines in the Müller-Lyer illusion appear unequal?

The surrounding arrow-like features provide contextual cues that alter the brain's interpretation of the lines. Learned experience with three-dimensional environments may contribute to this perceptual effect.

How can culture and individual characteristics influence chemical senses?

Cultural experience can affect how people identify odors and judge their pleasantness or intensity. Personality and attitudes can also influence taste preferences and evaluations of foods, including foods labeled as reduced-fat.