Vision: Receptors. Modes of Perception. Vision: Summary 9/28/2012. How do we perceive our environment? Sensation and Perception Terminology

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1 How do we perceive our environment? Complex stimuli are broken into individual features, relayed to the CNS, then reassembled as our perception Sensation and Perception Terminology Stimulus: physical agent that interacts with a receptor Receptor: structure that transduces a physical stimulus Transduction: process of converting a physical stimulus into a neural signal (sensation) Sensations: neural representation of physical stimuli Perceptions: cognitive interpretations of sensations Modes of Perception Vision: Receptors Bottom-up processing: our perceptions are the result of incoming sensations produced by physical stimuli Top-down processing: our perceptions are the result of experience, knowledge, bias, and contextual influences on incoming sensations Vision: Summary Auditory stimulus Stimulus: nm electromagnetic radiation Receptors: rods & cones (know the difference) Transduction: Light activates sends action potential through optic nerve to the brain Pathway: ½ of eye crosses to form contralateral visual field perceptions in each occipital lobe CNS Areas: occipital lobe - feature detectors (simple/complex cells) reassemble perception Perception: Influenced by top-down shortcuts Air pressure changes that unfold over time Three dimensions for the stimulus Frequency of the sound high versus a low sound Amplitude loudness of a sound Complexity how many frequencies are mixed together 400 Hz 1500 Hz 6 1

2 Auditory: Receptors Outer ear Middle ear Inner ear = receptors Auditory: Transduction The tectorial membrane bounces on the hair cells in rhythmic fashion to physically open ion channels and produce action potentials in the cochlear nerve Auditory: Afferent Signals Receptors in the cochlea are tuned to send action potential only for certain frequencies from high (outermost) to low (innermost). More receptors/ afferent signals for 500-5,000 Hz Each auditory cortex receives input from both ears BUT primarily from the contralateral ear. Neural signal goes to the primary auditory cortex in the temporal lobe. Auditory: Pathways Auditory: Perception (Left Brain) There are specialized brain regions for complex sounds and language. (secondary auditory cortex = language & music) Green = primary auditory cortex Brown = language comprehension area Gold = language production area Auditory: Perception (Right Brain) The same areas of the right hemisphere appear to be specialized to detect all environmental sounds other than language. 2

3 Auditory: Summary Stimulus: 20-20,000 Hz sound waves Receptors: Hair cells in the cochlea Transduction: Physical opening of ion channels in the cochlea by the tectorial membrane Afferent Signals: unevenly distributed to allow most signals for range of human speech Pathway: contralateral to primary auditory cortex CNS Areas: Temporal lobe; Wernickes, Brocas, and right hemisphere specializations Perception: Complex processing of language in the left hemisphere and music in the right hemisphere. The chemical senses... Taste and olfaction are grouped together as chemical senses because chemicals are the stimulus for both senses. PHYSICAL STIMULUS: Taste (gustatory system) stimuli are dissolved chemicals (in solution or saliva) Smell (olfactory system) stimuli are typically chemicals suspended in the air Olfactory Receptors Olfactory receptors are found in the back of the nasal cavity. (regenerate) Protected by mucous layer Olfactory receptors are modified neurons with cilia Olfactory Transduction Olfactory receptors are similar to the neurotransmitter receptors (both stimuli are chemicals, right?) Odorants fit only in certain receptors like a lock & key LOCK & KEY Olfactory: Signals LOCK & KEY Chemicals bind to the receptor causing a reaction in the neuron to send a neural signal to the olfactory bulb Each odor has its own pattern of activity Olfactory: Pathways & CNS Areas What is your perception of odors? Olfactory bulb to: Amygdala emotional value of stimuli Frontal Lobe memories, moods 3

4 Olfactory Perception Projections to the limbic system and frontal lobe closely link smell with memories and emotions Evolutionary pressure to remember harmful stimuli strong long-term memory mechanism Olfaction is a powerful component to flavor linked with gustation (taste). Olfactory: Summary Stimulus: Chemicals in air from nostrils or mouth Receptors: Olfactory receptor neurons with lock & key shape binding Transduction: Binding actives sending signal Afferent Signals: Odors produce unique patterns Pathway: Olfactory bulb Amygdala & Frontal Lobe CNS Areas & Perceptions: Amygdala (emotional value), Frontal Lobe (memory association), Orbitofrontal cortex (flavor perception) Gustatory: Receptors Taste buds are found on the surface of the tongue Gustatory: Transduction Chemicals dissolve in saliva and enter the taste bud pits Chemicals are interact with receptors on the taste receptor cells Taste cells release neurotransmitters on afferent taste neurons 3 sensory nerves relay taste sensations to the brain Insular cortex = primary taste quality (between the temporal & parietal lobes) Columns of neurons for salt, sour, sweet, bitter and umami Gustatory: Pathways Many secondary areas Gustatory: CNS Areas Limbic system & Frontal Lobe Hypothalamus hunger & satiety 4

5 Flavor Perception Flavor - the overall perception of an oral stimulant Includes taste, smell, texture, temperature, even color & appearance % subjects correctly identify flavored solutions Black bars = normal Gray bars = pinched nose Gustatory: Summary Stimulus: Chemicals in saliva or solutions Receptors: Taste receptor cells in taste buds Transduction: Different for each taste category Afferent Pathway: 3 nerves from oral cavity to the NST of the brainstem CNS Areas & Perceptions: Insular cortex (primary taste categories), Amygdala (cravings and aversions), Frontal Lobe (memory association), Hypothalamus (hunger & satiety) Orbitofrontal cortex (flavor perception) Touch: Somatosensory Many types of specialized receptors! Somatosensory: Transduction Mechanoreceptors (Meisners, Merkel, Ruffini, Pacinian, and Hair cells): physical movement opens ion channels to depolarize the neuron and send action potentials to the brain Bare or Free Nerve endings: detect increases or decreases in temperature and chemicals released in response to tissue damage (like histamines) (pain detection) 27 Pain Perception Pain following injury is often 2 sensations: Sharp immediate pain - myelinated neurons Dull throbbing secondary pain - unmyelinated neurons Speed difference due to myelin on axons! Immediate Sensation Delayed Sensation Overall Perception Somatosensory: Summary Stimulus: mechanical, thermal, and chemical Receptors: Mechanoreceptors & Free nerve endings Transduction: Physical movement, change in temp, or chemicals released by tissue damage Afferent Pathway: Dorsal column pathway for touch, anterolateral pathway for temp and pain CNS Areas & Perceptions: Postcentral gyrus is the primary somatosensory cortex (touch organized by body part); anterior cingulate gyrus (pain) 5

6 Psychophysics Psychophysics is the study of the our perceptions (behavior) to physical stimuli The first field of experimental psychology! Two types of thresholds: Absolute: can you detect a stimulus or not? Difference: can you detect a change in a stimulus? Difference Thresholds Usually our perception of stimuli does not exactly match changes in the actual stimulus Weber s law provided an equation to quantify (& predict) changes in perceptions based on changes in stimuli 1800s 1 st quantification of brain activity! 6