1 / 66

Understanding Sensation and Perception: The Role of the Senses

This chapter explores the fundamental concepts of sensation and perception, defining sensation as the raw experience of stimuli like light and sound, while perception involves interpreting these stimuli based on prior learning and expectations. It delves into how our senses have evolved as adaptations for survival, including the sophisticated detection of chemicals, light, sound, and tactile sensations. The chapter also describes psychophysical methods for measuring thresholds of perception and introduces key theories like Signal Detection Theory, emphasizing the interplay between sensory processes and decision-making.

karen-armstrong
Télécharger la présentation

Understanding Sensation and Perception: The Role of the Senses

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related