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Chapter 7

Chapter 7. Sensation. Sensation. The raw experience of a sensory stimulus, such as a light or sound Perception: The interpretation of sensory information according to expectations and prior learning. The Senses as Evolved Adaptations. Sensing Tastes and Smells

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Chapter 7

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  1. Chapter 7 Sensation

  2. Sensation • The raw experience of a sensory stimulus, such as a light or sound • Perception: The interpretation of sensory information according to expectations and prior learning

  3. The Senses as Evolved Adaptations • Sensing Tastes and Smells • sensitivity to chemicals important for feeding and reproduction • chemical receptors became more sophisticated • Smell vs. Taste receptors evolved

  4. The Senses as Evolved Adaptations • Sensing Light • responsiveness to the sun’s energy • provides “remote guidance” for sensing things at a distance • eyes allow us to process form, color, movement and visual acuity

  5. The Senses as Evolved Adaptations • Sensing Sounds • sensing sound increases range of sensation beyond that of smell • allows localization and identification • sound can be used as a form of communication

  6. The Senses as Evolved Adaptations • Sensing Touch, Warmth and Pain • skin senses allow location of nearby objects • touch enables skilled movements • pain motivates behavior

  7. Psychophysics • The study of how humans and animals respond to sensory stimuli • The mathematical relationship of sensory intensity to the magnitude of a physical stimulus

  8. Just Noticeable Difference (JND) • The minimal amount of sensory change in a stimulus that can be detected • e.g. how much more weight do you need to perceive a difference in weights?

  9. Just Noticeable Difference • Weber’s Law: jnd = kI • Just Noticeable Difference = Constant x Intensity • The size of the just noticeable difference is equal to some some proportion of the standard • Constant varies depending on sensory modality

  10. Just Noticeable Difference • Fechner: JND is a measure of the “psyche” • similar to inches on a ruler

  11. 100 Threshold = 50% response point 50 P(yes) 0 Stimulus Intensity The Absolute Threshold • Minimum amount of stimulation that can be detected on half the trials • Count up number of “yes” responses (Frequency of “seeing”)

  12. Psychophysical Methods: How to Measure Thresholds • Method of Limits • Start with a low intensity stimulus, gradually increase until observer reports a sensation (ascending) • Start with a high intensity, gradually decrease until observer no longer reports a sensation (descending) • Problems: • observer may not pay attention on low intensity trials • observer may anticipate stimulus on descending series

  13. Psychophysical Methods: How to Measure Thresholds • Method of Constant Stimuli • Present stimuli in a random order • observer cannot predict whether stimulus is above or below threshold

  14. Method of Magnitude Estimation • Stevens: • Observers use numbers to describe the perceived intensity of a stimulus • Relationship between stimulus intensity and magnitude estimates follows a power function

  15. Signal Detection Theory • The detection of a stimulus involves decision processes as well as sensory processes • Observers responses will change with motivation • e.g. paid $1 for each detection of stimulus results in a greater number of detections

  16. Signal Detection Matrix Judgment “Yes” “No” Hit Present Miss Stimulus False Alarm Correct Rejection Absent

  17. Signal Detection Matrix Pay $1 for each detection Judgment “Yes” “No” Hit Present Hit Miss Stimulus False Alarm Correct Rejection Absent

  18. Signal Detection Matrix Judgment Deduct $2 for each False Alarm “Yes” “No” Hit Present Miss Miss Stimulus False Alarm Correct Rejection Absent

  19. Two-Point Limen • A measure of tactile sensitivity • Sensitivity differs for different body areas • Sensitivity corresponds with Sensory Homunculus

  20. Subliminal Perception • Perception of stimuli below the absolute threshold • e.g. very briefly flashing messages • no evidence for effectiveness in advertising • However, flashed words can “prime” awareness of other stimuli • e.g. “bread” - “butter”

  21. A Five-Stage Modelof Sensory Systems • Each sensory system must have: 1. An adequate stimulus 2. Receptors adapted to the stimulus 3. Nerve pathways 4. Destination points in the brain 5. The psychological experience

  22. Seeing • The Stimulus: The Visible Spectrum • The portion of the electromagnetic spectrum between 400 to 700 nanometers

  23. The Eye • The eye focuses light on the retina • Retina: multilayered structure on the inner surface of the eye

  24. Transduction • The conversion of energy from one type to another • The eye transduces light energy into neural energy at the retina • Transduction occurs at the photoreceptors: • Rods: dim-light receptors • Cones: bright-light receptors

  25. The Retina • Photoreceptors receive light • Neural signal sent to Bipolar Cells. • Signal then sent to Retinal Ganglion Cells • Ganglion cells send signal out the eye to the brain • exit point is a “blind spot

  26. The Retina

  27. The Retina • Cones: • Located in the center of the retina • Often see a single cone connecting to a single ganglion cell • Rods: • Located in the periphery of the retina • Often see many rods connecting to a single ganglion cell

  28. Visual Nerve Pathways • Axons of ganglion cells for the optic nerve pathway • Optic nerve sends signals to the lateral geniculate nucleus (LGN) of the thalamus • Signals are then sent to the primary visual cortex in the occipital lobe • primary visual cortex = striate cortex

  29. Conscious vs. Non-conscious Visual Pathways • Retina - LGN - Striate cortex: “conscious visual pathway” • “Non-conscious pathways”: • Retina - Superior Colliculus: Responsible for perception of peripheral movement • Retina - Pretectum: Responsible for changing pupil size when presented with bright light.

  30. Dark Adaptation • An increase in visual sensitivity as a result of time spent in the dark • Sensitivity appears to plateau at 10 minutes, but then starts to increase again at 15 minutes • Rod-Cone Break

  31. Dark Adaptation

  32. Color Vision: Trichromatic Theory (Young-Helmholtz) • Color vision results from the activity of three cone pigments, each maximally sensitive to on of three wavelengths • Trichromatic Theory explains additive color mixing - the mixing of colored lights to create other colors • Dichromatism: color blindness resulting from missing one of three color receptors

  33. Color Vision: Opponent Process Theory (Hering) • Colors are sensed by “opponent pairs” • Red-Green • Blue-Yellow • White-Black • Can be used to explain negative afterimages

  34. Color-Opponent Cells • Ganglion cells are connected to photoreceptors such that they respond in an opponent process fashion to color • e.g. inhibited by green and excited by red

  35. Hearing • The Stimulus: Sound Waves • a wave of compressed air resulting from vibration

  36. Sound Waves • Waves of air that can vary in amplitude and frequency

  37. Sound as a Wave • Amplitude (intensity): related to psychological dimension of loudness • Frequency: related to psychological dimension of pitch • Complexity: related to psychological dimension of timbre

  38. Amplitude • Determined by size of wave • Measured in decibels (dB)

  39. Frequency • Determined by number of waves per second • Measured in Hertz (Hz)

  40. The Ear • Three Parts: • The Outer Ear • The Middle Ear • The Inner Ear

  41. The Ear

  42. The Outer Ear • Consists of • Pinna • Auditory Canal • Tympanic Membrane (Eardrum) • Main Function: • Gather sounds to send to middle and inner ear

  43. The Middle Ear

  44. The Middle Ear • Ossicles: Transfer and amplify sound to inner ear • Malleus (Hammer) • Incus (Anvil) • Stapes (Stirrup) • Oval Window • To inner ear

  45. Inner Ear (Cochlea) • Sound vibrations enter at oval window • Travel through fluid, vibrating basilar membrane

  46. Organ of Corti • Where sound is transduced into a neural signal • Sound is transduced by Hair Cells • Cilia on hair cells contact tectorial membrane • As basilar membrane vibrates, hair cells are pulled and neural signal is generated

  47. Flowchart of the Ear and Other Things Mechanical Vibrations (Eardrum & ossicles amplify) Pressure Waves (Cochlear Fluid) Ripples (Basilar Membrane) Airborne Vibrations Neuro-transmitter (Auditory Nerve Fibers) Electrical Charges (Hair cells) Bending (Cilia) Brain

  48. Place Theory: How we perceive pitch • Sound waves generate vibration in cochlear fluid and basilar membrane - travelling wave • Frequency of sound is encoded by the stimulation of specific place on basilar membrane • High frequencies cause vibrations at thin part of basilar membrane near oval window • Low frequencies cause vibrations at thicker part

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