Sensation & Perception Chapter 4 PDF

Sensation & Perception Chapter 4 PSYC 1110 04 Fall 2024 Overview and learning objectives Describe the neural basis of sensation and perception Describe the differences in sensory systems Understand how attention impact perception The cascade of sensory processing… Compl...

Sensation & Perception Chapter 4 PSYC 1110 04 Fall 2024 Overview and learning objectives Describe the neural basis of sensation and perception Describe the differences in sensory systems Understand how attention impact perception The cascade of sensory processing… Complex cascade of information processing Sense organs act as transducers ○ Physical stimulus → neural activity Transduction → sensation → perception Adaptation Neurons and sensory change their sensitivity (and selectivity) with experience ○ Dark adaptation in the visual system Occurs when a stimulus remains constant over time ○ Olfactory system (smell) adapts very quickly Perceptual features are selected based on importance or relevance ○ Innate features of the sensory system, but shaped by experience Selection https://doi.org/10.1371/journal.pone.0020162 Feature detectors Feature detectors are “tuned” based on experience. Coding Threshold of stimulation required for perception ○ E.g., adding 1 candle to room with no candles VS a room with 1000 candles In the brain, stimulation is coded only by the sensory system that is activated ○ E.g., pressure on your eye is coded as a visual perception Synesthesia as a unique case of cross-coding in sensory systems Perceptual thresholds What’s the relationship between the physical stimulus and your experience? ○ Gustav Fechner, psychophysics Absolute thresholds of perception Gradual shift in perceptual recognition ○ Biases, motivation, and thresholds Signal detection to distinguish sensitivity Difference thresholds Just-noticeable difference (JND) ○ Minimum change in stimulus in order for you to detect the change 50% of the time Weber’s law ○ Perception of stimulus changing is proportional to the magnitude of the stimulus In a quiet room → you can whisper.2 (background noise) / 2 (volume of speech) =.1 In a loud room → you have to shout.5 (background noise) / 5 (volume of speech) =.1 Physical visual properties Wavelength Brightness Structure of the eye Cornea - bend light inward toward lens Pupil - hole in iris (muscle) Eye muscles - accommodation to lens Lens - accommodation to focus light on fovea Retina - light sensitive photoreceptors Optic nerve - axons projection to the brain  Visual transduction Rods - photoreceptors sensitive to dim light ○ Only produce black and white sensations ○ Most sensitive to light Cones - photoreceptors sensitive to colors and fine detail Blind spot ○ Where optic nerve passes out of the eye Fovea ○ Large concentration of only cones in middle of retina ○ Highest visual acuity Peripheral vision ○ Mediated by rods adjacent to fovea ○ Highly sensitive to motion and “seeing” in dim light Rods and cones RODS CONES ~ 120 million ~ 5 million All contain the same photopigment Contain 1 of 3 photopigments Most dense in periphery of retina Most dense around the fovea Specialize in sensitivity Specialize in acuity  Colour vision Colour is a psychological construct created by the brain ○ That are no actual colours in the stimuli we perceive ○ Stimuli have different capacities for absorbing/reflecting light ○ Experience of white light is an evolutionary adaptation Trichromatic theory of vision ○ 3 types of photopigments ○ Each cone is relatively more sensitive to either red, green, or blue  Colour vision Opponent-process theory ○ Cones respond as “either-or” to colour pairs Cones adaptation to a colour results in: ○ (1) reduced perception of the colour ○ (2) enhanced perception of opposing colour (reduced ability to inhibit opposing colour) Colour vision  Colour vision Opponent-process theory ○ Cones respond as “either-or” to colour pairs Cones adaptation to a colour results in: ○ (1) reduced perception of the colour ○ (2) enhanced perception of opposing colour (reduced ability to inhibit opposing colour) Complementary pairs of colours stand out more ○ Mutual inhibition  Colour vision Both theories are correct! ○ Trichromatic at the level of photoreceptors Responsivity is differentially sensitive to wavelength ○ Opponent-process at the level of the brain Perceptual experience is in colour-pairs  Object identification Hierarchical analysis and integration into complex percept ○ Optic chiasm - crossing of optic nerve from each eye ○ Thalamus - specialized nuclei for visual processing ○ Primary visual cortex - sensory receiving area in occipital lobe Retinotopically organized Association of visual information Highest visual association occurs in regions adjacent to temporal lobes ○ Integrates specificity, familiarity, discrimination and recognition Incomplete integration can lead to… ○ Visual agnosias (meaning, “not knowing” about some visual feature) Can perceive and draw a square, but do not recognize it as a square ○ Prosopagnosia Inability to perceive faces Dorsal and ventral visual pathways ? e i s it Wher Wha t is it? Dorsal and ventral visual pathways Distinct roles, but must integrate to support vision ○ Damage to dorsal pathway Individuals can see/recognize object, but cannot reach out to grab it Middle temporal cortex ○ Specialized cells ○ Perceive motion ○ Each neuron tuned to specific direction of movement How do we hear? Pinna Tympanic membrane Auditory ossicles ○ Malleus ○ Incus ○ Stapes Oval window Cochlea Organ of corti Stereocilia How do we hear? Video Link - Auditory Transduction Theories of hearing Frequency theory ○ Sound wave frequency corresponds to firing rate of nerve impulses Place theory of pitch ○ Higher/lower frequencies stimulate specific parts of the cochlea Pitch & loudness Frequency theory ○ Describes perception of low-pitched sounds Place theory of pitch ○ Describes perception of high-pitched sounds The place-frequency maps in primary auditory cortex Localization of sound Input from each ear facilitates localization through… ○ timing (which comes first) ○ intensity (which is louder) Hearing loss Conductive ○ Issue with external ear in transferring vibrations ○ Often treatable with hearing aid Sensorineural ○ Issue with inner ear hair cells or auditory nerve ○ Often due to noise-induced hearing loss Somatosensory cortex Topographical representation of body senses ○ Cortex dedicated based on importance/sensitivity Perception influenced by expectation Skin senses Merkel’s disk - pressure Free nerve ending - warmth, cold, pain Meissner’s corpuscles - pressure Hair follicle - hair movement Pacinian corpuscles - pressure and vibration Ruffini’s endings - skin stretching Skin senses - pain Sensitivity is related to density of receptors Large nerve fibres - carry fast, sharp pain signals ○ Warning system Small nerve fibres - nagging, aching, widespread (chronic) pain ○ Reminding system Skin senses - pain receptor types and function Skin senses - pain Video Link - Nociceptors Skin senses - pain Gate control theory ○ Different fibres pass through “gate” in spinal cord ○ One type of pain can override another Proprioception Awareness of body position at rest ○ Cells keep track of where body parts are relative to one another Vestibular system maintains sense of balance ○ Head movement causes shift in fluids ○ Signals send to cerebellum Kinesthetics ○ Sense and movement of body through space Interoception Receptors that provide internal sensation from bones and organs ○ Insular cortex ○ Feedback about internal physiological state Association between insula activity and awareness https://www.nature.com/articles/nn1176 Olfaction (smell) Smell receptors respond to airborne molecules Detection based on “matching” of molecules to specific receptor sites ○ Combination of odour receptors (can detect 10,000) ○ Location of receptors ○ Number of activated receptors ○ Arrangement of cells in epithelium is seemingly random Some individuals experience anosmia ○ Infection ○ Head trauma ○ Exposure to chemicals Olfaction (smell) Spherical clusters of glomeruli are not randomly distributed ○ Organized by receptor type Stimulation of these neuron clusters aids in discrimination of potentially trillions of odors Gustation (taste) Chemical sense, evolutionary adaptations for certain tastes Five basic sensations for taste ○ Bitter ○ Sour ○ Salt ○ Sweet ○ Umami Taste (perception) is heavily influenced by smell, texture, and temperature Perceptual modes of processing Bottom-up ○ Building perception from units of sensations Low level features Additive Top-down ○ Building perception from higher-level organization Pre-existing knowledge Past experience Top-down and face processing Faces are processed holistically ○ Individual features are less useful Gestalt organizing principles The whole is greater than the sum parts ○ Simplest organization involves grouping ○ Principles provide basic plans for organization Figure-ground is extremely powerful and likely innate Gestalt organizing principles Closure ○ Illusory figures (shapes/objects are implied) Depth perception Ability to see 3-D space and judge distance Observable as early as 2 weeks of age Depth cues Binocular ○ Depth and distance info requiring two eyes Monocular ○ Depth and distance info required one eye Binocular depth cues Retinal disparity Eyes receive slightly different, but overlapping input from their respective visual fields. Binocular depth cues Convergence Change of focus for objects that are close. Monocular depth cues Accomodation ○ Bending lens to focus on close objects Pictorial depth ○ Creates illusion of depth from 2-D images Perceptual hypothesis We actively construct meaningful perceptions Perceptual hypothesis Conflicting information is impossible to resolve Cannot form a valid hypothesis Perceptual constancies You need experience and knowledge of objects to judge size and distance Our perceptions maintains constancy, despite changes in sensory information ○ Size, shape, brightness, colour Perceptual sets & learning Same sensory information can lead to different perception(s) ○ Mental predisposition → top-down influencing bottom-up Experience and context as a guide Perceptual learning ○ Language ○ Face processing Moving from sensation to perception Perception is shaped by mental constructs ○ Experience Illusions reveal perceptual misconstructions ○ Length, position, motion, direction, etc. ○ Distortion between internal and external information Hallucinations as distorted perceptions ○ Mismatch from external reality Moving from sensation to perception Video Link - Visual Illusion