Sensation and Perception

Sensation and Perception

• Sensation involves gathering information through sense organs and translating external energy into internal representations for processing by the brain.
• Perception is the creative process of selecting, organizing, and interpreting sensory input, constructing a phenomenological world from sensory experiences.

Basic Principles

• There is no direct correlation between physical stimuli and psychological experiences; the relationship is non-random.
• Sensation and perception are active and adaptive processes shaped by evolutionary pressures, guiding attention to relevant environmental aspects.
• Human infants show a natural inclination to focus on patterns resembling human faces.

Psychophysics

• A branch of psychology examining the relationship between physical attributes and psychological experiences.
• Key findings could aid in restoring sensory functionalities, such as vision.

Sensing the Environment

• Transduction converts physical stimuli into neural impulses, enabling sensory signals to reach the brain.
• Each sense has a specific threshold, below which stimuli remain undetected despite external presence.
• Constant decision-making is essential for distinguishing meaningful stimuli from irrelevant noise.

Transduction

• Transduction is the mechanism by which physical energy is transformed into neural impulses, coded by intensity (neuron firing frequency) and quality (type of receptors affected).
• Sensory receptors are specialized cells that respond to environmental energy and generate action potentials.

Absolute Thresholds

• Defined as the minimum physical energy required for a stimulus to be detected roughly 50% of the time.
• Psychological factors like expectations and motivation can influence sensory thresholds.

Signal Detection Theory

• Sensation involves not just detection but also the judgment of stimulus presence.
• It includes two processes: sensory detection and decision-making, alongside the potential for errors in reporting stimuli.

Difference Thresholds and Just Noticeable Difference (jnd)

• The difference threshold is the minimum change in stimulus intensity required for a person to notice a difference.
• jnd is influenced by the intensity of pre-existing stimuli, as described by Weber's Law, which states that the perceived difference is a constant proportion of the stimulus.

Fechner's and Stevens' Laws

• Fechner's Law indicates that subjective experience increases logarithmically with actual stimulus intensity.
• Stevens' Power Law suggests that perceived intensity grows arithmetically while actual stimulus magnitude increases exponentially.

Sensory Adaptation and Subliminal Perception

• Sensory adaptation allows receptors to become less responsive to unchanged stimuli, while subliminal perception occurs outside conscious awareness and does not prompt conscious processing.

Vision

• Light, as electromagnetic radiation, is focused by the eye to create visual representations in the brain.
• Wavelength, frequency, and amplitude of light correlate with color, hue, and brightness.

Eye Structure and Function

• Light passes through the cornea, aqueous humor, pupil, lens, and vitreous humor before reaching the retina, where transduction occurs.
• The retina consists of photoreceptors (rods and cones), with rods sensitive to dim light and cones responsive to color and detail.

Photoreceptors

• Rods provide black, white, and gray visual sensations, while cones specialize in color and require more light to function.
• Rods are more prevalent in peripheral vision, while cones are concentrated in the fovea, enabling sharp detail perception.

Visual Pathway

• Visual information travels from the retina through the optic nerve to the brain, processing stimuli in separate pathways for spatial and object recognition.
• The occipital lobe is crucial for interpreting visual information, including color, form, and motion.

Colour Perception

• Colour perception is psychological, contingent upon hue, saturation, and lightness, relying on three types of cones sensitive to specific wavelengths.
• The Trichromatic theory and Opponent-process theory explain color vision at different processing levels in the retina and brain, respectively.### Nature of Sound
• Sound consists of vibrations in air molecules; sound waves are acoustic energy that travel at approximately 340 m/s.
• Sound waves reflect off surfaces, creating echoes, and are absorbed by materials, leading to muffled sounds.
• Key properties of sound waves include frequency, complexity (timbre), and amplitude.

Frequency

• Defined as the number of cycles per second (measured in Hertz, Hz).
• Pitch corresponds to frequency; higher frequency equals higher pitch. Doubling frequency results in a pitch an octave higher.
• Human hearing range is approximately 15 to 20,000 Hz, with music typically ranging from 16 Hz to over 4,000 Hz.

Complexity (Timbre)

• Complexity refers to the mix of frequencies in a sound, affects its distinctive quality (timbre) and is created by both fundamental frequencies and overtones.

Amplitude and Loudness

• Amplitude indicates the wave's height, correlating with loudness; greater amplitude results in louder sounds.
• Amplitude is measured in decibels (dB); 0 dB marks the minimum hearing threshold, and sounds over 130 dB can be painful.

Ear Structure

• Outer Ear: Comprises the pinna, which helps locate sounds, and the auditory canal, approximately 2.5 cm long.
• Middle Ear: Contains the eardrum (tympanic membrane) and three tiny bones (ossicles: malleus, incus, stapes) that transmit vibrations.
• Inner Ear: Houses the cochlea, responsible for sound transduction; comprises fluid-filled chambers and hair cells, which initiate sensory signals.

Sound Transduction Process

• Sound waves travel through the ear, resonating in the auditory canal, vibrating the eardrum, and moving ossicles.
• Vibrations reach the oval window, creating pressure waves in cochlear fluid, bending hair cells that convert mechanical energy into neural signals.

Hearing Loss

• Conduction loss: Issues in the external or middle ear impede sound transmission.
• Sensorineural loss: Damage to inner ear receptors or auditory pathways affects sound perception.
• Exposure to high noise levels can lead to permanent hearing damage.

Pitch Perception Theories

• Place Theory: Explains high-frequency pitch perception; different pitches activate specific areas along the basilar membrane.
• Frequency Theory: Accounts for low-frequency pitch perception; the rate of basilar membrane vibrations correlates with perceived frequency.

Neural Pathways of Hearing

• Auditory information travels from the inner ear through the cochlea to the medulla, integrating signals in the brain, and ultimately reaching the auditory cortex.

Sound Localization

• Based on differences in loudness and timing between the ears, aided by binaural neurons that integrate auditory signals with visual cues.

Other Senses Overview

• Vision and audition are highly specialized, with other senses including olfaction (smell), gustation (taste), and somatosensory (touch).

Smell (Olfaction)

• Distinguishes dangers and detects familiar scents; relies on approximately 10 million receptors in the nasal cavity.
• Transduction occurs in olfactory epithelium, with information processed through the olfactory nerve, bypassing the thalamus.

Taste (Gustation)

• Sensitive to soluble substances; taste receptors are found in approximately 10,000 taste buds on the tongue.
• Taste functions through a dual pathway to identify flavors and elicit emotional responses, with basic tastes including sweet, sour, salty, and bitter.

Skin Senses and Touch

• Skin functions as a multi-layered organ, providing touch perception via receptors for pressure, temperature, and pain.
• Phantom limb sensations arise when sensory systems reorganize post-injury, leading to misperceived sensations.

Pain Perception

• Pain serves a protective function; transduction involves free nerve endings that transmit pain signals.
• Gate-control theory suggests that the brain regulates pain perception via interactions among different nerve fibers, influenced by mental states.### Pain Control
• Small axons transmit neural information slowly, making pain messages susceptible to inhibition by faster A-fibre sensory inputs.
• Distraction techniques, including pleasant views, can increase pain tolerance; hypnosis also aids in pain management.
• Pain perception is influenced by beliefs, expectations, and emotional states.

Proprioceptive Senses

• Proprioceptive senses gather information about body position and movement, integrated with touch and vision.
• Kinesthetic receptors in joints inform about limb positioning, while muscle and tendon receptors relay muscle tension.

Vestibular Sense

• The vestibular sense detects body position in space, leveraging gravity and movement, with organs located in the inner ear.
• Semicircular canals sense acceleration in any direction; vestibular sacs monitor gravity.
• Hair cells in vestibular organs respond to movements and transmit impulses to parts of the hindbrain like the cerebellum.
• Vection, a sensory illusion, can cause individuals to feel motion when their surroundings move.

Depth Perception

• Depth and distance perception is organized through binocular cues (from both eyes) and monocular cues (from one eye).
• Binocular cues include retinal disparity and convergence; monocular cues involve interposition, elevation, and texture gradient.
• Motion parallax aids depth cues, where nearby objects appear to move faster than distant ones.

Motion Perception

• Motion detection relies on ganglion cells that react to changes in visual stimuli.
• The neural pathway for motion perception starts in the retina and travels through the thalamus to motion-sensitive neurons in the primary visual cortex.
• Area MT (medial temporal) processes object movement directionally.

Perceptual Constancy

• Perceptual constancy maintains stable perception of size, shape, and color despite changes in sensory input.
• Size constancy ensures objects appear the same size from different distances.
• Color constancy allows objects to maintain perceived color despite changes in lighting.

Perception Organization

• Perceptual organization involves integrating sensations into meaningful units (percepts) and locating them in spatial context.
• Form perception organizes sensations into shapes and patterns, guided by Gestalt principles like figure-ground perception and proximity.

Recognition-by-Components

• Object identification involves matching stimuli against stored perceptual memories categorized by component parts (geons).
• This method allows rapid recognition and categorization of objects.

Sensory Processes and Interpretation

• Sensory experience interpretation is reliant on memory and prior experience, developing innate potential with environmental input.
• Bottom-up processing starts with raw data, while top-down processing is influenced by context and expectations.

Theories of Hearing

• Auditory perception involves sound waves that create air particle vibrations; cycles of air expansion define sound wave frequency (pitch).
• Place theory correlates specific frequencies with different basilar membrane areas, while frequency theory relates membrane rate to sound frequency.

Taste and Smell

• Olfaction involves invisible gas molecules detected by receptors in the olfactory epithelium, influencing complex scents.
• Gustation relies on receptors in tastebuds that transduce soluble molecules into neural signals.

Touch Perception

• Touch includes pressure, temperature, and pain, relying on various receptor types throughout the body.
• Reflexive actions are initiated by sensory neurons that connect to spinal nerves, transmitting touch information to the somatosensory cortex.

Perceptual Set

• Perceptual set is shaped by experience, context, and motivation, influencing how stimuli are interpreted.
• Experience with the environment creates expectations, guiding perception through both bottom-up and top-down processes.