1.6 Sensation
- Syllabus
- 2025
- Topic
- 1.6
- Level
- —
Learning objectives
1.6A—Explain how the process of sensation is related to behavior and mental processesExplain how the process of sensation is related to behavior and mental processes.• Sensation is the process of detecting information from the environment that meets a certain threshold and transducing stimuli into neurochemical messages for processing (perception) in the brain. The absolute threshold occurs when a stimulus can be detected at least 50% of the time.• Detection of change in stimuli or diminished sensitivity to stimuli can be explained by the just-noticeable difference and sensory adaptation. Weber’s law describes the degree to which stimuli need to be different for the difference to be detected.• The sensory systems constantly work together in a process called sensory interaction. Synesthesia is an experience of sensation in which one system of sensation is experienced through another.1.6B—Explain how the structures and functions of the visual sensory system relate to behavior and mental processes.…Explain how the structures and functions of the visual sensory system relate to behavior and mental processes. UNIT 1 Biological Bases of Behavior• The retina is the photosensitive surface at the back of the eye. Cells in the retina capture visual information that is transduced to the brain for processing. Evidence of incomplete images captured by the retina is demonstrated by the presence of the blind spot, where the visual nerve exits the eye. The brain fills in the gaps in the incomplete retinal images to perceive a relatively complete picture of the world.• Visual stimuli are focused onto the retina by the lens via a process called accommodation. When this process is altered, nearsightedness or farsightedness can result.• Cells that lie in the periphery of the eye and detect shapes and movement, but not color, are called rods. These cells are mainly activated in low-light environments. These cells play a role in light and dark adaptation.• Color vision is explained by both the trichromatic theory and the opponent-process theory.- i. Photoreceptor cells located in the fovea of the eye that process color and detail are called cones. Researchers have identified blue (detecting short wavelengths), green (detecting medium wavelengths) and red (detecting long wavelengths) cones in the retina.- ii. Afterimages result when certain ganglion cells in the retina are activated while others are not. The ganglion cells involved in this opponent process are red/green, blue/ yellow/ and black/white.- iii. Color vision deficiency involves damage or irregularities to one or more cones or ganglion cells (red/green, blue/ yellow). Color vision deficiency includes dichromatism or monochromatism.• Damage to parts of the brain responsible for vision (mainly the occipital lobes) can result in disorders such as prosopagnosia (face blindness) and blindsight.1.6C—Explain how the structures and functions of the auditory sensory system relate to behavior and mental processesExplain how the structures and functions of the auditory sensory system relate to behavior and mental processes.• Sound occurs through the movement of air molecules at different wavelengths (called pitch) and amplitudes (called loudness).• Theories that help explain pitch perception include place theory, volley theory, and frequency theory.• Sound localization describes how we identify where sounds in our environment are coming from.• Hearing difficulties can result from aging and various kinds of damage to auditory structures. Types of hearing loss include conduction deafness and sensorineural deafness.1.6D—Explain how the structures and functions of the chemical sensory systems relate to behavior and mental processesExplain how the structures and functions of the chemical sensory systems relate to behavior and mental processes.• Structures in the nose and brain process and/ or transduce olfactory stimuli. Smell is the only sense not processed first in the thalamus of the brain. Pheromones produce chemical messages for the olfactory system.• Gustation is the sense of taste, and types of tastes include sweet, sour, salty, bitter, umami, and oleogustus.• Structures in the tongue, mouth, and brain process and/or transduce basic tastes. The number of taste receptors on the tongue is related to how sensitive people are to tastes, classifying them as supertasters, medium tasters, or nontasters.• The chemical senses interact to create the sensation of taste. Without the sense of smell, taste sensations are either muted or not experienced.1.6E—Explain how the structures and functions of the touch sensory system relate to behavior and mental processesExplain how the structures and functions of the touch sensory system relate to behavior and mental processes.• Structures within the skin and brain process and/or transduce touch stimuli. The sensation of “hot” is produced by the activation of warm and cold receptors in the skin. WLEDGE1.6F—Explain how the structures and functions of the pain sensory system relate to behavior and mental processesExplain how the structures and functions of the pain sensory system relate to behavior and mental processes.• Pain is processed both in the body and in the brain. Gate control theory is one attempt to describe the complexities of pain. Phantom limb sensation occurs when people who have lost limbs report sensation or pain where the limb used to be.1.6G—Explain how the structures and functions that maintain balance (vestibular) and body movement (kinesthetic)…Explain how the structures and functions that maintain balance (vestibular) and body movement (kinesthetic) relate to behavior and mental processes.• The vestibular sense controls balance and is primarily detected by the semicircular canals and structures in the brain.• Kinesthesis the sense of one’s body movement. Kinesthesis allows the body to move in coordinated ways without having to look at the various parts of the body as it moves. 46 AP PSYCHOLOGY UNIT 2 Cognition 15–25% AP EXAM WEIGHTING ~17–23 CLASS PERIODS 47 | Remember to go to AP Classroom to assign students the online Progress Check for this unit. Whether assigned as homework or completed in class, the Progress Check provides each student with immediate feedback related to this unit’s topics and skills. Progress Check 2 Multiple-choice: ~25 questions Free-response: 2 questions
From Stimulus to Sensation
Sensation begins when a sensory system detects environmental information that reaches a threshold. Transduction then converts the stimulus into neurochemical messages; the brain processes those messages in perception. Sensation is therefore the input-and-conversion stage, while perception is the brain’s processing of that input.
| Idea | What it explains |
|---|---|
| Absolute threshold | The intensity detected at least 50% of the time |
| Just-noticeable difference | The smallest detectable change between stimuli |
| Weber’s law | How different two stimuli must be for their difference to be detected |
| Sensory adaptation | Reduced sensitivity during continuing stimulation |
Sensory systems do not operate in isolation. Sensory interaction occurs when systems work together to shape experience. Synesthesia is a distinct experience in which stimulation of one sensory system is experienced through another.
A threshold is not a fixed line that guarantees detection every time: the absolute-threshold definition uses 50% detection. Adaptation also does not mean the stimulus disappeared; sensitivity to it diminished.
How Vision Becomes a Percept
The lens focuses visual stimuli onto the retina by accommodation. The retina is the photosensitive surface at the back of the eye; its cells transduce captured information into signals for the brain. Where the visual nerve exits, the retina has a blind spot, so the captured image is incomplete and the brain fills the gap. Altered accommodation can produce nearsightedness or farsightedness.
| Receptor | Location/conditions | Main contribution |
|---|---|---|
| Rods | Mainly peripheral retina; active in low light | Shape and movement, not color; light/dark adaptation |
| Cones | Fovea | Color and detail; short-, medium-, and long-wavelength sensitivity associated with blue, green, and red |
| Theory | Evidence relationship |
|---|---|
| Trichromatic | Color vision uses three cone sensitivities |
| Opponent-process | Ganglion-cell pairs operate as red/green, blue/yellow, and black/white; unequal activation helps explain afterimages |
The theories address different stages and can both contribute to color vision. Damage or irregularities in cones or ganglion cells can produce dichromatism or monochromatism. Brain damage, especially involving occipital processing, can produce prosopagnosia or blindsight even when the eye receives stimulation.
Sound: From Air Movement to Hearing
| Physical sound pattern | Experienced quality |
|---|---|
| Wavelength | Pitch |
| Amplitude | Loudness |
Air-molecule movement reaches the auditory system and is processed as sound. Place theory, frequency theory, and volley theory are complementary attempts to explain pitch perception; they should be identified as explanations of how physical sound patterns become experienced pitch, not as types of sound.
Sound localization is the process of identifying where an environmental sound originates. Hearing difficulty may result from aging or damage to auditory structures. AP Psychology distinguishes conduction deafness from sensorineural deafness as different categories of hearing loss.
Pitch is linked to wavelength and loudness to amplitude; reversing those pairs is a common error. Localization asks where a sound comes from, not how high, low, loud, or quiet it is.
Smell and Taste Build Flavor Together
| Chemical sense | Main structures and route | Key distinctions |
|---|---|---|
| Olfaction | Nose and brain process/transduce odor chemicals | The only sense not processed first in the thalamus; pheromones are chemical messages for this system |
| Gustation | Tongue, mouth, and brain process/transduce taste chemicals | Basic tastes: sweet, sour, salty, bitter, umami, and oleogustus |
Taste sensitivity is related to the number of taste receptors on the tongue. This relationship supports the classifications supertaster, medium taster, and nontaster.
Experienced flavor depends on sensory interaction. Gustatory signals supply basic taste information while olfactory signals contribute smell; when smell is unavailable, taste sensations may be muted or absent.
Taste and flavor are not interchangeable. Taste refers to gustatory categories, while the fuller experience of flavor depends on interaction between taste and smell.
Touch Is Constructed from Receptor Signals
Touch begins when structures in the skin detect and transduce physical stimulation. Signals are then processed in the brain, linking contact with a conscious touch experience and an appropriate behavioral response.
The sensation described as ‘hot’ illustrates combination rather than a single one-to-one receptor label: it is produced by activation of both warm and cold receptors in the skin.
A sensation need not come from one receptor type acting alone. ‘Hot’ is an experienced result built from a pattern of receptor activity and brain processing.
Pain Is Processed by Body and Brain
Pain is processed both in the body and in the brain. It is therefore not a direct meter of tissue input alone: bodily signals and central processing jointly shape the experience and the behavior that follows.
| Idea | What it contributes |
|---|---|
| Gate control theory | One attempt to explain why pain signals can be modulated rather than experienced as a fixed copy of stimulation |
| Phantom-limb sensation | Sensation or pain can be reported where a lost limb used to be, showing the importance of brain processing |
Phantom-limb pain is a real sensory experience even though the limb is absent. It does not show that pain is imaginary; it shows that pain processing involves more than receptors at the current site of a limb.
Balance and Body Position Use Different Senses
| Sense | Main information | Structures or use |
|---|---|---|
| Vestibular sense | Balance | Detected primarily by the semicircular canals and brain structures |
| Kinesthesis | Movement and position of one’s body | Supports coordinated movement without visually monitoring each body part |
Remaining upright depends mainly on vestibular balance information. Moving an arm accurately without watching it depends on kinesthetic information about body movement. Ordinary coordinated action can use both systems at once, but they supply different kinds of information.
Do not use vestibular and kinesthetic as synonyms: vestibular sensation concerns balance, whereas kinesthesis concerns the body’s movement and position.