MS

Sensation and Perception

Sensation and Perception

Sensation

  • Sensation and perception are parts of one continuous process.
  • Sensation:
    • Sensory receptors and nervous system receive and represent stimulus energies from our environment.
    • Senses receive sensory stimulation, transform it into neural impulses, and deliver this information to the brain.

Transduction

  • Conversion of one form of energy into another.
  • In sensation, it transforms stimulus energies (sights, sounds, smells) into neural impulses the brain can interpret.

Absolute Threshold

  • Minimum stimulus energy needed to detect a particular stimulus 50% of the time.
  • Tested by defining the point where half the time a stimulus is detected and half the time it is not.
  • Subliminal: Input below the absolute threshold for conscious awareness.
  • Priming: Activating associations in our mind, often unconsciously, setting us up to perceive, remember, or respond to objects or events in certain ways.

Basic Concepts

  • Difference threshold:
    • Minimum difference a person can detect between any two stimuli half the time.
  • Weber’s law:
    • For an average person to perceive a difference, two stimuli must differ by a constant minimum percentage (not a constant amount).

Subliminal Messages

  • Subliminal stimuli:
    • Too weak to detect 50 percent of the time; below the absolute threshold.
  • Subliminal sensation:
    • Exists, but such sensations are too fleeting to enable exploitation with subliminal messages.
  • Subliminal persuasion:
    • May produce a fleeting and subtle but not powerful or enduring effect on behavior (Greenwald, 1992).

Sensory Adaptation

  • Diminished sensitivity because of constant stimulation.
  • Aids focus by reducing background chatter.
  • Influences how the world is perceived in a personally useful way.

Perception

  • Perception: Brain organizes and interprets sensory information, enabling us to recognize objects and events as meaningful.

Bottom-Up vs Top-Down Processing

  • Bottom-up processing:
    • Begins with the sensory receptors and works up to the brain’s integration of sensory information.
  • Top-down processing:
    • Guided by higher-level mental processes.
    • Construct perceptions drawing on our experience and expectations.

Perceptual Set

  • Mental predisposition to perceive one thing and not another.
  • Affects top-down processing.
  • What determines our perceptual set?
    • Schemas organize and interpret unfamiliar information through experience.
    • Preexisting schemas influence top-down processing of ambiguous sensation interpretation, including gender stereotypes.

Influence of Motivation and Emotions

  • Walking destinations look farther away when we are fatigued.
  • Slopes look steeper when we are wearing a heavy backpack (or after listening to sad, heavy classical music).
  • Water bottles look closer when we are thirsty.

Perceiving Vision

  • Our eyes receive light energy and transduce (transform) it into neural messages.
  • Our brain then creates what we consciously see.

Wavelengths

  • Wavelength: distance from one wave peak to the next.
  • Hue: color experienced.
  • Amplitude: height.
  • Intensity: amount of contained energy; influences brightness.

Light Reflection

  • Components:
    • Pupil
    • Iris
    • Retina
    • Lens
    • Cornea
    • Blind spot
    • Fovea (point of central focus)
    • Optic nerve to brain's visual cortex

Rods and Cones

  • Cones are sensitive to detail and color.
  • Rods are sensitive to faint light.
  • Light energy triggers chemical changes in the rods and cones which activate the bipolar cells.
  • These cells then activate the ganglion cells of the optic nerve, which transmits the neural impulses from the eye to the brain.

Retinal Processing

  • Optic nerve: Carries neural impulses from the eye to the brain; highway from eye to brain.
  • Blind spot: The point at which the optic nerve leaves the eye, where no receptor cells are located.
  • Fovea: The central focal point in the retina, around which the eye’s cones cluster.

Color Theories

  • Young-Helmholtz trichromatic (three-color) theory:
    • Eye must have three corresponding color receptor types, each sensitive to red, green, and blue wavelengths.
    • Color is seen when light stimulates these cones.
    • Color-deficient vision; colorblind.
  • Hering’s hypothesis (opponent-process theory):
    • Opposing retinal processes (red-green, blue-yellow, white-black) enable color vision.
    • Cones’ responses are then processed by opponent-process cells.
    • Afterimages.

Feature Detection

  • Specialized nerve cells in the brain respond to specific features of the stimulus, such as shape, angle, or movement.
  • Cells receive information from the ganglion cells in the retina and pass the information to other cortical areas, where teams of cells (supercell clusters) respond to more complex patterns.

Parallel Processing

  • Brain’s ability to do many things simultaneously.
  • Visual scene is first divided into subdimensions: form, depth, motion, perceptual constancy.

Grouping

  • Perceptual tendency to organize stimuli into coherent groups:
    • Proximity: Grouping nearby figures together.
    • Continuity: Perceiving smooth, continuous patterns, rather than discontinuous ones.
    • Closure: Filling in gaps to create a complete, whole object.

Depth Perception

  • Ability to see objects in three dimensions, although the images that strike the retina are two-dimensional.
  • Allows us to judge distance.
  • Is present, at least in part, at birth in humans and other animals.

Early 3-D Perception

  • Most infants refuse to crawl across the visual cliff.
  • Crawling, no matter when it begins, seems to increase an infant's fear of heights.

Cues for Depth

  • Two eyes help with perception of depth.
    • Binocular cues.
  • Depth cue (i.e., relative height and size available to either eye alone).
    • Monocular cues.

Perceptual Constancy

  • Objects are perceived as unchanging (having consistent color, brightness, shape, and size), even as illumination and retinal images change.
  • Color constancy: Seeing the color of familiar items as being constant.
  • Brightness constancy: Depends on context.
  • Shape constancy: Seeing that familiar items' shapes are constant.
  • Size constancy: Recognizing objects as being the same size despite changes in distance.

Sound

Sound Waves

  • Amplitude (height) determines intensity (loudness) in sound waves.
    • Intensity \propto Amplitude^2
  • Length (frequency) determines the pitch.
    • Pitch: Tone’s experienced highness or lowness (depends on frequency).
  • Sound is measured in decibels (dB).
  • Low frequency = long wavelength = low pitch.
    • f = \frac{v}{\lambda}, where f is frequency, v is wave velocity and \lambda is wavelength

Characteristics of Sound Waves

  • Bands of compressed and expanded air.
  • Human ears detect these changes in air pressure and transform them into neural impulses.
  • Brain decodes these changes as sound.
  • Vary in amplitude and frequency differing loudness differing pitch.

Waves and Sounds

  • The shorter the wavelength, the higher the frequency.
  • Wavelength determines the pitch of sound.
  • Wave amplitude influences sound intensity.

The Ear

  • Vibrating air (sound waves) enters the outer ear and passes through the auditory canal to the eardrum.
  • Middle ear: Amplifies the vibrations of the eardrum.
  • Cochlea: Contains nerve receptors.
  • Inner ear: Innermost part of the ear.

Decoding Sound Waves

  • Sound waves strike the eardrum, causing it to vibrate.
  • Tiny bones in the middle ear pick up the vibrations and transmit them to the cochlea.
  • Ripples in the fluid of the cochlea bend the hair cells lining the surface, which trigger impulses in nerve cells.
  • Axons from these nerve cells transmit a signal to the auditory cortex.

Hearing Loss

  • Sensorineural hearing loss (nerve deafness):
    • Damage to cell receptors or associated nerves.
  • Conduction hearing loss:
    • Damage to the mechanical system that conducts sound waves to the cochlea.
  • Cochlear implant:
    • A device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea.

Hearing Different Pitches (Theories)

  • Place theory:
    • Links the pitch heard with the place where the cochlea’s membrane is stimulated; best explains high pitches.
  • Frequency theory (temporal theory):
    • The rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling its pitch to be sensed; explains low pitches.

Sound Location

  • Sound waves strike one ear sooner and more intensely than the other.
  • From this information, the brain can compute the sound’s location.

Five Senses (Touch, Taste, Smell)

Touch

  • Sense of touch is a mix of four distinct skin senses:
    • Pressure
    • Warmth
    • Cold
    • Pain
  • Other skin sensations are variations of these basic four.
  • Cognition influences the sensory responses of the brain.

Pain

  • Biopsychosocial phenomenon that varies widely from group to group and person to person.
  • Influences of pain (biological, psychological, social-cultural).
  • Gate-control theory:
    • The spinal cord contains a neurological “gate” that either blocks pain signals or allows them to pass on to the brain.

Biopsychosocial Model & Pain

  • Biological influences:
    • Activity in spinal cord's large and small fibers
    • Genetic differences in endorphin production
    • The brain's interpretation of CNS activity
  • Psychological influences:
    • Attention to pain
    • Learning based on experience
    • Expectations
  • Social-cultural influences:
    • Presence of others
    • Empathy for others' pain
    • Cultural expectations

Senses: Taste (Gustation)

  • Involves several basic sensations.
  • Can be influenced by learning, expectations, and perceptual bias.
  • Has a survival function.
  • A chemical sense:
    • Sweet: Energy source
    • Salty: Sodium essential to physiological processes
    • Sour: Potentially toxic acid
    • Bitter: Potential poisons
    • Umami: Proteins to grow and repair tissue

Senses: Smell (Olfaction)

  • A chemical sense.
  • Olfactory receptor cells: Located in the olfactory bulb in the nose.
  • A combination of several odor molecules stimulates different receptors to detect them.
  • Patterns are interpreted by the olfactory cortex.
  • Gender, age, and expertise influence the ability to identify and remember scents.