Chapter 4: Sensation & Perception

Sensation and Perception: The Distinction Sensation: a process by which our sensory receptors and nervous system receive and represent stimulus energy Perception: selection, organization, and interpretation of sensory input. Enables us to recognize meaningful things Psychophysics = the study of how physical stimuli are translated into psychological experience Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Distinction between Sensation & Perception Ch.4- Sensation & Perception

Sensation vs Perception Ch.4- Sensation & Perception

Sensation: Principles Psychophysics: study of the relationship between physical characteristics of stimuli & our psychological experience of them Fechner: the concept of the threshold Absolute threshold: detected 50% of the time Just noticeable difference (JND): smallest difference between 2, detectable 50% of the time Weber’s law: size of JND proportional to size of initial stimulus Weber’s Fraction: Applies to different types of sensory input Weight= 1/30 of an increase the JND becomes larger Ex: 30 ounces JND=1/90 ounces JND=3 Ch.4- Sensation & Perception

The Absolute Threshold 25 50 75 100 Low Absolute threshold Medium Intensity of stimulus Percentage of correct detections Subliminal stimuli When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal” Ch.4- Sensation & Perception

Psychophysics: Concepts and Issues Signal-Detection Theory: Sensory processes + decision processes Subliminal Perception: Existence vs. practical effects Sensory Adaptation: Decline in sensitivity to prolonged stimulation Ch.4- Sensation & Perception

Signal-detection theory Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Basics of Color Vision Wavelength determines color Longer = red / shorter = violet ROY G BIV Amplitude determines brightness Purity determines saturation Additive Color Mixing: Light/White Subtractive Color Mixing: Paint/Black Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Wavelength Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Amplitude Ch.4- Sensation & Perception

Light, the Physical Stimulus for Vision Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The color solid Ch.4- Sensation & Perception

Additive vs. Subtractive Color Mixing Ch.4- Sensation & Perception

The Eye: Converting Light into Neural Impulses Eye Components: Cornea: where light enters the eye Lens: focuses the light rays on the retina Accommodation=adjusting (Close=Round Far=Flatten) Iris: colored ring of muscle, constricts or dilates via amount of light Pupil: regulates amount of light Process: Cornea-Pupil-Iris-Fovea-Retina-Optic Nerve Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Human Eye Ch.4- Sensation & Perception

The Retina: An Extension of the CNS Retina: absorbs light, processes images to the brain Optic disk: optic nerve connection/blind spot Receptor cells: 20/1 Rods: black and white/low light vision Cones: color and daylight vision Adaptation: becoming more or less sensitive to light as needed Dark Adaptation: eye becomes more sensitive to light, 30 min Light Adaptation: eye becomes less sensitive to light Information processing: Receptive fields: the retinal area, when stimulated, affects the firing of that cell Lateral antagonism: when neural activity in a cell opposes activity in surrounding cells Ch.4- Sensation & Perception

Nearsightedness & Farsightedness Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Retina Ch.4- Sensation & Perception

The Process of Dark Adaptation Ch.4- Sensation & Perception

The Retina and the Brain: Visual Information Processing Light  rods and cones  neural signals  bipolar cells  ganglion cells  optic nerve  optic chiasm  opposite half brain Main pathway: lateral geniculate nucleus (thalamus)  primary visual cortex (occipital lobe) Second pathway: superior colliculus  thalamus  primary visual cortex Ch.4- Sensation & Perception

Visual Pathways Through the Brain Ch.4- Sensation & Perception

The what and where pathways from the primary visual cortex Ch.4- Sensation & Perception

Hubel and Wiesel: Feature Detectors and the Nobel Prize Early 1960’s: Hubel and Wiesel Microelectrode recording of axons in primary visual cortex of animals Discovered feature detectors: neurons that respond selectively to lines, edges, etc. Groundbreaking research: Nobel Prize in 1981 Later research: cells specific to faces in the temporal lobes of monkeys and humans Ch.4- Sensation & Perception

Visual Information Processing Abstraction: Brain’s higher-level cells respond to combined information from feature- detector cells Feature detection: Brain’s detector cells respond to elementary features-bars, edges, or gradients of light Retinal processing: Receptor rods and cones bipolar cells ganglion cells Recognition: Brain matches the constructed image with stored images Scene Ch.4- Sensation & Perception

Theories of Color Vision Trichromatic theory - Young and Helmholtz Receptors for red, green, blue – color mixing (TV) Opponent Process theory – Hering 3 pairs of antagonistic colors red/green, blue/yellow, black/white After Image Effect: image persist after a stimulus is removed Current perspective: both theories necessary Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Afterimage Effect Ch.4- Sensation & Perception

Ch.4- Sensation & Perception

Hearing: The Auditory System Stimulus = sound waves (vibrations of molecules traveling in air) Amplitude (loudness) Wavelength (pitch) Purity (timbre) tone’s highness or lowness Wavelength described in terms of frequency: measured in cycles per second (Hz) Frequency increase = pitch increase Ch.4- Sensation & Perception

Sound, the physical stimulus for hearing Ch.4- Sensation & Perception

The Ear: Three Divisions External ear (pinna): collects sound -> Tympanic Membrane (ear drum) Middle ear: the ossicles (hammer, anvil, stirrup) Inner ear: the cochlea a fluid-filled, coiled tunnel contains the hair cells, the auditory receptors lined up on the basilar membrane Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Human Ear Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Basilar Membrane Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Auditory Pathway Sound waves vibrate bones of the middle ear Stirrup hits against the oval window of cochlea Sets the fluid inside in motion Hair cells are stimulated with the movement of the basilar membrane Physical stimulation converted into neural impulses Sent through the thalamus to the auditory cortex (temporal lobes) Ch.4- Sensation & Perception

Theories of Hearing: Place or Frequency? Hermann von Helmholtz (1863) Place theory: Pitch corresponds to vibrations of different places along the basilar membrane Other researchers (Rutherford, 1886) Frequency theory: Pitch corresponds to the frequency of the entire basilar membrane vibrates Georg von Bekesy (1947) Traveling wave theory: Pitch corresponds in a wave (incorporates place & frequency theories) Ch.4- Sensation & Perception

Auditory Localization: Where Did that Sound Come From? Two cues critical: Intensity (loudness) Timing of sounds arriving at each ear Head as “shadow” or partial sound barrier Timing differences as small as 1/100,000 of a second Ch.4- Sensation & Perception

Cues in Auditory Localization Ch.4- Sensation & Perception

The Chemical Senses: Taste Taste (gustation) Physical stimulus: soluble chemical substances Receptor cells found in taste buds Pathway: taste buds -> neural impulse -> thalamus -> cortex Four primary tastes: Sweet Sour Bitter Salty Taste: learned and social processes Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Tongue & Taste Ch.4- Sensation & Perception

The Chemical Senses: Smell Smell (Olfaction) Physical stimuli: Chemicals carried in the air dissolved in fluid, the mucus in the nose Olfactory receptors = olfactory cilia Pathway: Information is gathered from chemicals in the air. Inhaled molecules excite receptors in the olfactory epithelium. The olfactory bulb gathers messages from the olfactory receptor cells and sends them to the brain Olfactory cilia -> neural impulse -> olfactory nerve -> olfactory bulb (brain) -Does not go through thalamus Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Olfactory System Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Skin Senses: Touch Physical stimuli = mechanical, thermal, and chemical energy impinging on the skin. Pathway: Sensory receptors -> the spinal column -> brainstem -> cross to opposite side of brain -> thalamus -> somatosensory (parietal lobe) Temperature: free nerve endings in the skin Pain receptors: also free nerve endings Two pain pathways: fast vs. slow Ch.4- Sensation & Perception

Pathways for Pain Signals Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Pain Gate Control Theory The spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain “gate” opened by the activity of pain signals traveling up small nerve fibers “gate” closed by activity in larger fibers or by information coming from the brain Ch.4- Sensation & Perception

Other Senses: Kinesthetic & Vestibular Kinesthesis - knowing the position of the various parts of the body Receptors in joints/muscles Vestibular - equilibrium/balance Semicircular canals Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Reversible figures: drawing with 2 interpretations that can shift back & forth *Perception of the World is Highly Subjective* Perceptual sets: (Expectations) Inattentional blindness/Selective Attention: Expectations lead you to focus on a particular thing Feature detection theory - bottom-up processing Form perception - top-down processing Subjective contours: perception of contours where none exist Gestalt psychologists: the whole is greater than the sum of its parts Ch.4- Sensation & Perception

A Famous Reversible Figure Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Necker cube Ch.4- Sensation & Perception

Feature Analysis in Form Perception Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Subjective Contours Ch.4- Sensation & Perception

Principles of Perception Gestalt principles of form perception: Figure-ground Proximity Similarity Continuity Closure Simplicity Common fate: objects moving in the same direction belong together Recent research: Distal (stimuli outside the body) Proximal (stimulus energies impinging on sensory receptors) Perceptual hypotheses Context. Which distal stimulus is responsible for proximal stimulus sensed Ch.4- Sensation & Perception

Perceptual Organization Figure and Ground organization of the visual field into objects (figures) that stand out from their surroundings (ground) Ch.4- Sensation & Perception

Gestalt Principles of Perceptual Organization Ch.4- Sensation & Perception

Distal & Proximal Stimuli Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Context Effects Ch.4- Sensation & Perception

Depth & Distance Perception Binocular cues – clues from both eyes together Retinal disparity: Difference between vision in both eyes Convergence: Focus on object close eye turn inward Monocular cues – clues from a single eye Motion parallax: Images at different distances moving at different rates Pictorial depth cues Linear Perspective Texture Gradient Interposition Relative Size Height in Plane Light/Shadow Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Depth Cues Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Relative Size Ch.4- Sensation & Perception

Ch.4- Sensation & Perception Interposition Ch.4- Sensation & Perception

Stability in the Perceptual World: Perceptual Constancies Perceptual constancies – stable perceptions amid changing stimuli Size Shape Brightness Hue Location in space Ch.4- Sensation & Perception

Optical Illusions: The Power of Misleading Cues Optical Illusions - discrepancy between visual appearance and physical reality Famous optical illusions: Muller-Lyer Illusion Ponzo Illusion Poggendorf Illusion Upside-Down T Illusion Zollner Illusion The Ames Room Impossible Figures Ch.4- Sensation & Perception

The Muller-Lyer illusion Ch.4- Sensation & Perception

Explaining the Muller-Lyer Illusion Ch.4- Sensation & Perception

Ch.4- Sensation & Perception The Ames Room Ch.4- Sensation & Perception

Four Geometric Illusions Ch.4- Sensation & Perception

Three Classic Impossible Figures Ch.4- Sensation & Perception