Unit 1: Biological Bases of Behavior

Module 1.6A: Sensation: Basic Concepts

Learning Targets

• LT 1.6-1: Explain the three steps that are basic to all of our sensory systems.

• LT 1.6-2: Explain the difference between absolute thresholds and difference thresholds.

• LT 1.6-3: Explain the function of sensory adaptation.

LT 1.6-1: Basic Steps in Sensory Systems

• Sensation: The process whereby sensory receptors and the nervous system receive and represent stimulus energies from the environment.

• Sensory Receptors: Sensory nerve endings which respond to stimuli, allowing the intake of information from the environment.

• Function of Sensation: Sensation allows the perception of the world as it provides the stimuli that are then processed and interpreted by the brain.

• Face Blindness (Prosopagnosia): An example illustrating the difference between sensation and perception; individuals can see faces (sensation) but are unable to recognize them as faces (perception).

• Perception: The organizing and interpreting of sensory information by the brain, enabling recognition of objects and events.

• Information Processing:

  • Bottom-Up Processing: Starts with sensory receptors and builds up to brain interpretation.

  • Top-Down Processing: Starts with expectations based on experiences and works down to interpret sensory input.

• Transduction: The conversion of one form of energy into another; in sensation, it is the conversion of physical energy (sights, sounds, smells) into neural impulses.

• Psychophysics: The study of the relationship between the physical characteristics of stimuli and our psychological experiences of them.

• Basic Tasks of Sensory Systems: Receive information, transform energies, and deliver information to the brain.

LT 1.6-2: Absolute and Difference Thresholds

• Absolute Threshold: The minimum stimulus energy required to detect a particular stimulus 50 percent of the time.

  • Example: Gustav Fechner’s Research: Investigated how much stimuli is necessary for detection and established the concept of absolute thresholds.

• Signal Detection Theory: Predicts how and when we detect faint stimuli (signals) amid background noise, suggesting that detection depends on experience, expectations, motivation, and alertness rather than a fixed threshold.

• Subliminal: Refers to stimuli below the absolute threshold for conscious awareness.

• Difference Threshold (Just Noticeable Difference - JND): The minimum difference between two stimuli required for detection 50 percent of the time.

  • Weber's Law: States that to perceive differences, two stimuli must differ by a constant minimum percentage, not a fixed amount.

  • Example: For light intensity changes, the difference must be 8% to notice a change in brightness.

LT 1.6-3: Sensory Adaptation

• Sensory Adaptation: Diminished sensitivity to constant stimulation; upon continuous exposure to an unchanging stimulus, awareness diminishes.

  • Mechanism: Occurs because nerve cells fire less frequently over time with constant exposure.

  • Example in Vision: Despite constant visual stimuli, the adaptation prevents our sight from disappearing due to the constant movement of our eyes, which refreshes the stimuli.

  • Importance: Sensory adaptation allows us to focus on meaningful stimuli while ignoring constant distractions, highlighting the utilitarian perceptions we hold of the world around us.

Module 1.6B: Sensation: Vision

Learning Targets

• LT 1.6-4: Explain the characteristics of visible light and the eye structures involved in focusing that energy.

• LT 1.6-5: Describe how rods and cones process information and the path information takes from the eye to the brain.

• LT 1.6-6: Explain how we perceive color in our environment.

• LT 1.6-7: Describe the function and location of feature detectors.

• LT 1.6-8: Explain how the brain utilizes parallel processing to construct visual perceptions.

LT 1.6-4: Characteristics of Visible Light

• Wavelength: The distance between the peaks of light waves, determining color; shorter wavelengths equate to blue (high frequency) and longer wavelengths to red (low frequency).

• Hue: The color dimension determined by the wavelength of light.

• Intensity: The amount of energy in a light wave which influences perceived brightness, related to the amplitude of the wave.

• Eye Structures:

  • Cornea: The clear, protective outer layer of the eye, covering the pupil and iris.

  • Pupil: The adjustable opening through which light enters.

  • Iris: The colored muscle controlling the size of the pupil opening.

  • Lens: A transparent structure that adjusts shape to focus light onto the retina (Accommodation).

  • Retina: Contains rods and cones; the inner surface where light is converted into neural signals.

LT 1.6-5: Rods and Cones Processing

• Rods: Detect black, white, and gray; sensitive to motion and necessary for twilight and peripheral vision.

• Cones: Concentrated in the fovea; function in well-lit conditions; detect fine detail and cause color sensations.

• Pathway: Rods and cones activate bipolar cells leading to ganglion cells. The optic nerve, formed by the axons of ganglion cells, transports visual information to the brain.

• Blind Spot: The area where the optic nerve exits the eye, void of receptor cells.

LT 1.6-6: Perception of Color

• Young-Helmholtz Trichromatic Theory: Proposes three types of color receptors sensitive to red, green, blue; combinations allow the perception of various colors.

  • Color perception is a combination of stimulation across the three types of cones.

  • Color blindness issues arise due to deficiencies in these cones.

• Opponent-Process Theory: Proposes that color perception is controlled by opposing retinal processes (red-green, blue-yellow, white-black).

• Afterimage Effect: Staring at one color can create an afterimage in the opposing color upon shifting focus.

LT 1.6-7: Feature Detectors

• Feature Detectors: Nerve cells in the visual cortex that respond to specific characteristics such as shape, angle, and movement.

  • These detectors help to process incomplete images, reassembling them into coherent perceptions (like puzzles).

• Fusiform Face Area: A specific area in the brain responsible for recognizing faces from varying angles.

LT 1.6-8: Parallel Processing

• Parallel Processing: The brain's method of processing multiple aspects of stimuli simultaneously (like color, movement, shape).

• This processing occurs unconsciously and is essential for interpreting sensory signals accurately; damage to specific processing areas can lead to deficits in perception, such as inability to detect motion.

Module 1.6C: Sensation: Hearing

Learning Targets

• LT 1.6-9: Describe characteristics of sound waves.

• LT 1.6-10: Explain how the ear transforms sound energy into neural impulses.

• LT 1.6-11: Discuss how we detect loudness and pitch, as well as sound location.

LT 1.6-9: Characteristics of Sound Waves

• Audition: Sense of hearing, vital for communication and adaptability.

• Frequency: Number of wavelengths passing a point in a given time, related to pitch.

• Amplitude: The height of sound waves, correlating to loudness; louder sounds have higher amplitudes.

• Decibels: Measured loudness; sounds over 85 decibels may cause hearing damage.

LT 1.6-10: Sound Transformation in the Ear

• Middle Ear: Contains bones (hammer, anvil, stirrup) that transmit vibrations from the eardrum to the cochlea.

• Cochlea: A fluid-filled structure triggering neural impulses when sound waves pass through; contains hair cells on the basilar membrane that respond to sound waves.

• Pathway to Brain: Sound waves cause the eardrum to vibrate, which is transferred through middle ear bones to the cochlea, activating hair cells that trigger nerve signals to travel down the auditory nerve to the temporal lobe's auditory cortex.

LT 1.6-11: Loudness, Pitch, and Sound Location

• Loudness: Related to the number of activated hair cells; higher loudness activates more cells.

• Pitch Perception Theories:

  • Place Theory links pitch perception to the location of stimulation on the cochlea's membrane.

  • Frequency Matching Theory states that the rate of nerve impulses along the auditory nerve matches the tone's frequency.

• Locating Sounds: Use of two ears to differentiate between sound intensity and timing; sound shadows assist in pinpointing direction.

Module 1.6D: Sensation: Skin, Chemical, and Body Senses; Sensory Interaction

Learning Targets

• LT 1.6-12: Explain basic touch sensations and how we sense touch.

• LT 1.6-13: Compare biological, psychological, and social factors affecting pain; explain placebo and distraction's role in pain management.

• LT 1.6-14: Explain the senses of taste and smell.

• LT 1.6-15: Explain how we sense body position and movement.

• LT 1.6-16: Explain sensory interaction and embodied cognition.

LT 1.6-12: Touch Sensations

• Touch: A crucial tactile sense promoting well-being; requires skin contact from birth for growth and comfort.

• Four Basic Touch Sensations: Pressure, warmth, cold, and pain; various combinations lead to other sensations like tickling or itching.

• Sensory Cells: Different cells in the skin respond to heat, cold, and pressure variably; cognitive factors influence sensations (e.g., touch from different individuals elicits different responses).

LT 1.6-13: Pain Experience

• Gate-Control Theory: A theory stating that a neurological gate in the spinal cord can block or allow pain signals to reach the brain. Pain signals travel through small fibers, while large fibers can inhibit these signals.

• Biospsychosocial Phenomenon: Pain perception involves biological (nociceptors), psychological (emotional state), and social-cultural (context) factors.

• Placebos: Can effectively reduce pain due to belief in their efficacy; distraction techniques can further alleviate perceived pain.

LT 1.6-14: Taste and Smell

• Gustation (Taste): Involves five basic tastes critical for survival (sweet, salty, sour, bitter, umami) processed by taste buds on the tongue; expectations can influence perceived taste quality.

• Olfaction (Smell): The oldest chemical sense; bypasses the thalamus with receptors in the nasal cavity detecting a plethora of smells with a strong association with memory and emotional recall; anosmia pertains to the loss of smell ability.

LT 1.6-15: Body Position and Movement

• Kinesthesis: The sense of body position and movement; proprioceptors in muscles, joints, and tendons provide this feedback.

• Vestibular Sense: Helps maintain balance and spatial orientation; semicircular canals detect fluid movement in the inner ear to provide balance information.

LT 1.6-16: Sensory Interaction and Embodied Cognition

• Sensory Interaction: One sense may influence another, augmenting our perceptions (e.g., smell enhancing taste).

• Embodied Cognition: Suggests that bodily sensations can influence cognitive processes, connecting sensory experiences deeply with cognitive evaluations.

Summary of Sensory Systems

Sources: Myers/DeWall/Yost Hammer, Myers’ Psychology for the AP® Course, 4e © BFW Publishers