chapter 4

Chapter 4

Sensation and Perception

Slides prepared by: Melissa S. Terlecki, Cabrini College

PSYCHOLOGYSchacterGilbertWegner

PSYCHOLOGYSchacterGilbertWegner

4.1

The Doorway to Psychology

Figure 4.1: Synesthesia (p. 90)

Questions

What role does the brain play in what we see and hear?

Sensation

Synesthesia: the perceptual experience of one sense that is evoked by another sense. psychological and neurobiological evidence.

Sensation: simple awareness due to the stimulation of a sense organ.

Perception: the organization, identification, and interpretation of a sensation in order to form a mental representation.

Transduction: when sensors in the body covert physical signals from the environment into neural signals sent to the nervous system.

Culture and Community: Our Brain Interpret Messages…

Cultural differences (Japanese and American participants) in relative versus absolute tasks of sensation and perception.experiment in line drawing.

Psychophysics

Scientific investigation requires objective measures, but behavior must be operationalized; quantify perception.

Psychophysics: methods that measure the strength of a stimulus and the observer’s sensitivity to that stimulus.experiments involving making judgments.

Questions

Why is the perception of any event unique to yourself?

Measuring Thresholds

Absolute threshold: the minimal intensity needed to just barely detect a stimulus. threshold: a boundary. difference between “sensing” and “not sensing”. detection on 50% of experimental trials.

Just noticeable difference (JND): the minimal change in a stimulus that can just barely be detected.

Weber’s Law: the just noticeable difference of a stimulus is a constant proportion despite variations in intensity.

Table 4.1: Approximate Sensory Thresholds (p. 92)

Signal Detection

Sensing is gradual, not all-or-none. Noise: all other stimuli coming from the

internal and external environment. can compete and interfere.

Signal detection theory: an observation that the response to a stimulus depends both on a person’s sensitivity to the stimulus in the presence of noise and on a person’s response criterion. errors: hits, misses, false alarms, and correct

rejections.

Questions

How accurate and complete are our perceptions of the world?

Cluttered Environments (p. 93)

Sensory Adaptation

Sensory adaptation: sensitivity to prolonged stimulations tends to decline over time as an organism adapts to current conditions.stimulus doesn’t change.

Questions

What conditions have you already adapted to today? sounds?smells?

The Real World: Multitasking

Selective attention impairs multitasking when sudden reaction is required.driving and multitaksing: reaction time

experiments.more impaired for complex or novel tasks.

PSYCHOLOGYSchacterGilbertWegner

4.2

Vision: More Than Meets the Eye

Vision

Visual acuity: the ability to see fine detail.smallest font

readable from 20 feet away in humans (20/20 is perfect).

The Snellen Eye Chart, p. 96

Sensing Light

Visible light is the portion of the electromagnetic spectrum that we can see. light waves vary in wavelength.

length (hue), amplitude (brightness), number of wavelengths (purity).

Table 4.2: Properties of Light Waves (p. 96)

Figure 4.2: Electromagnetic Spectrum (p. 97)

The Human Eye

Parts of the eye include the cornea, pupil, iris, and retina.retina: light-sensitive tissue lining the back

of the eye that houses the receptors for detecting light.

Accommodation: the process by which the eye maintains a clear image on the retina.myopia: nearsightedness.hyperopia: farsightedness.

Figure 4.3: Anatomy of the Human Eye (p. 97)

Figure 4.4: Accommodation (p. 98)

Questions

How do eyeglasses actually correct vision?

Phototransduction in the Retina

Two types of photoreceptors in the retina. cones: detect color, operate under normal daylight conditions,

and allow us to focus on fine detail. rods: become active only under low-light conditions for night

vision. Fovea: an area of the retina where vision is the clearest

and there are no rods at all. Peripheral vision: lower acuity.

Layers of retina include rod and cone layers, but also bipolar and retinal ganglion cells (RGCs).

Blind spot: an area of the retina that contains neither rods nor cones and therefore has no mechanism to sense light, connects with the optic nerve.

Figure 4.5: Close-up of the Retina (p. 99)

Figure 4.6: Blind Spot Demonstration (p. 100)

Receptive Fields

Receptive field: the region of the sensory surface that, when stimulated, causes a change in the firing rate of that neuron.on-center cell: receptive field with a central

excitatory zone surrounded by an inhibitory zone.

off-center cell: receptive field with a central inhibitory zone surrounded by an excitatory zone.

Figure 4.7: RGC Receptive Fields Viewed End-on (p. 100)

Perceiving Color

Visible spectrum; most sensitive to red (long), green (medium), and blue (short) wavelengths. additive color mixing: increasing light to create

color. subtractive color mixing: removing light from the

mix. Color deficiency/color blindness: one or

more cone types is missing. Color afterimage: staring too long at one color can

cause sensory adaptation, a type of color deficiency.

Figure 4.8: Seeing in Color (p. 101)

Figure 4.9: Color Mixing (p. 101)

Figure 4.10: Color Afterimage (p. 102)

The Visual Brain

Outside of the eye, visual information travels to the lateral geniculate nucleus (LGN) in the thalamus to area V1 in the occipital cortex.area V1: the part of the occipital lobe that

contains the primary visual cortex.perceiving shapes, location, orientation, and

edges.

Figure 4.11: Visual Pathway from Eye Through Brain (p. 103)

Figure 4.12: Single Neuron Feature Detectors (p. 103)

Representing Objects and Faces in the Brain

Modular view: specialized brain areas, or modules, detect and represent objects and faces.

Distributed representation: pattern of activity across multiple brain regions that identifies any viewed object (including faces).

Visual-Form agnosia: the inability to recognize objects by sight.

Questions

How do we recognize our friends, even when they’re hidden behind sunglasses?

Principles of Perceptual Organization

Perceptual constancy: a perceptual principle stating that even as aspects of sensory signals change, perception remains constant.

Gestalt perceptual grouping rules: simplicity, closure, continuity, similarity, proximity, common fate.

Figure versus ground perception.size, movement, edge assignment.

Figure 4.13: Perceptual Grouping Rules (p. 105)

Figure 4.14: Ambiguous Edges (p. 106)

Perceiving Depth and Size

The visual world exists in length, width, and depth dimensions, but the retina only processes 2 dimensions (length and width) and thus must rely on depth cues.

Monocular depth cues: aspects of a scene that yield information about depth when viewed with only one eye. linear perspective, texture gradient,

interposition, relative height

Figure 4.15: Familiar Size and Relative Size (p. 106)

Figure 4.16: Pictorial Depth Cues (p. 107)

Perceiving Depth and Size

Binocular disparity: the difference in the retinal images of the two eyes that provides information about depth.

Illusions in depth perceptionAmes room.

Figure 4.17: Binocular Disparity (p. 108)

Figure 4.18: The Amazing Ames Room (p. 109)

Questions

What does the Ames room tell us about how the brain can be fooled?

Perceiving Motion

The visual system encodes information regarding space and time.MT region of temporal lobe.

Motion perception subject to illusions.waterfall illusion, phi phenomenon.apparent motion: the perception of

movement as a result of alternating signals appearing in rapid succession in different locations.

Questions

How can flashing lights on a casino sign give the impression of movement?

PSYCHOLOGYSchacterGilbertWegner

4.3

Audition: More Than Meets the Ear

Sensing Sound

Sound waves: changes in air pressure unfolding over time. described by frequency, amplitude, complexity. pitch: how high or low a sound is. loudness: a sound’s intensity. timbre: a listener’s experience of sound quality or

resonance.

Pure tone: a simple sound wave that first increases air pressure then creates a relative vacuum.

Table 4.3: Properties of Sound Waves (p. 111)

Questions

Why does one note sound so different on a flute and a trumpet?

The Human Ear

The human ear is divided into 3 parts: outer ear (pinna, auditory canal, eardrum), middle ear (ossicles), and the inner ear (cochlea).cochlea: a fluid filled tube that is the organ

of auditory transduction.basilar membrane: undulates when vibrations

from the ossicles reach the cochlear fluid.hair cells: specialized auditory receptor neurons

embedded in the basilar membrane.

Figure 4.19: Anatomy of the Human Ear (p. 112)

Questions

How do hair cells in the ear enable us to hear?

Figure 4.20: Auditory Transduction (p. 113)

Perceiving Pitch

Area A1: a portion of the temporal lobe that contains the primary auditory cortex. topographic organization. processes simple tones.

Two methods for encoding sound-wave frequency: place code: the cochlea encodes different

frequencies at different locations along the basilar membrane.

temporal code: the cochlea registers low frequencies via the firing rate of action potentials entering the auditory nerve.

Figure 4.21: Primary Auditory Cortex (p. 113)

Questions

How does the frequency of a sound wave relate to what we hear?

Localizing Sound Sources

Loudness and timing differences allow us to localize sound (stereophonic hearing).

PSYCHOLOGYSchacterGilbertWegner

4.4

The Body Senses: More Than Skin Deep

The Body Senses

Somatosenses: the body senses.Haptic perception: active exploration of

the environment by touching and grasping objects with our hands.

Touch

Four types of receptors located under the skin’s surface enable us to sense pressure, texture, pattern, and vibration.

Thermoreceptors sense cold and warmth and respond when skin temperature changes.

Figure 4.22: Touch Receptors (p. 115)

Questions

Why might discriminating spatial detail be important for fingertips and lips?

Pain

Tissue damage is transduced by pain receptors. A-delta fibers: transmit initial sharp pain. C-fibers: transmit longer-lasting, duller pain.

Referred pain: the feeling of pain when sensory information from internal and external areas converge on the same nerve cells in the spinal cord.

Gate-control theory: a theory of pain perception based on the idea that signals arriving from pain receptors in the body can be stopped or gated by interneurons in the spinal cord via feedback from 2 directions. bottom-up control. top-down control.

Questions

Why does rubbing an injured area sometimes help alleviate pain?

Self-amputation (p. 117)

Body Position, Movement, and Balance

Sensory receptors in the muscles, tendons, and joints provide information related to position, movement, and balance.

Vestibular system: the 3 fluid filled semicircular canals and adjacent organs located next to the cochlea in each inner ear.detects movement of the fluid when the

head moves or accelerates.

Questions

Why is it so hard to stand on one foot with your eyes closed?

PSYCHOLOGYSchacterGilbertWegner

4.4

The Chemical Senses: Adding Flavor

Smell (Olfaction)

Smell sensed through odorant molecules. pheromones: biochemical odorants emitted by

other members of a species that can affect an animal’s behavior or physiology.

Olfactory epithelium contains olfactory receptor neurons (ORNs): receptor cells that initiate the sense of smell.

Olfactory bulb: a brain structure located above the nasal cavity beneath the frontal lobes; collects axons from ORNs.

Figure 4.23: Anatomy of Smell (p. 119)

Questions

How many scents can humans smell?

Figure 4.24: Smell and Social Behavior (p. 120)

Taste (Gustation)

The tongue is covered with thousands of papillae which contain hundreds of taste buds (the organ of taste transduction).Microvilli: taste receptor tips that react with

tastant molecules in food.Taste system contains taste receptors

that detect 5 sensations: salt, sour, bitter, sweet, and umami.

Figure 4.25: A Taste Bud (p. 121)

Questions

Why is the sense of taste an evolutionary advantage?

Where Do You Stand: Perception and Persuasion

Subliminal advertising at movie theaters.Mixed evidence of effectiveness.

Sensory branding used today; associations made with pleasant sensations.

Ethics in (mis)leading perceptions?