Chapter 4: Sensation & Perception

Chapter 4: Sensation & Perception

1. Psychophysics

   • Sensation begins with stimulus, any detectable input from the environment
   • A threshold is a dividing point between energy levels that do and do not have a detectable effect
   • An absolute threshold for a specific type of sensory input is the minimum amount of stimulation that an organism can detect
   • Webers law states that the size of a just noticeable difference is a constant proportion of the size of the initial stimulus. This constant proportion is called Weber fraction
   • Fechner's law states that the magnitude of a sensory experience is proportional to the number of JNDs (unit of measurement) that the stimulus causing the experience is above the absolute threshold.
   • Signal detection theory proposes that the detection of stimuli involves decision processes as well as sensory processes, which are both influenced by a variety of factors besides stimulus intensity.
   • Subliminal perception is the registration of sensory input without conscious awareness.
   • Sensory adaptation is a gradual decline in sensitivity due to prolonged stimulation. It is an automatic, built-in process.

2. The Visual System

   • The lens is the transparent eye structure that focuses the light rays falling on the retina
   • Nearsightedness is when close objects are seen clearly but distant objects are blurry
   • Farsightedness is when distant objects are seen clearly but close objects appear blurry
   • The pupil is the opening in the centre of the iris that helps regulate the amount of light passing into the rear chamber of the eye
   • When we are looking at something, our eyes are scanning the visual environment and making brief fixations at various parts of the stimuli. These eye movements are referred to as saccades
   • The retina is the neural tissue lining the inside back surface of the eye; it absorbs light, processes images, and sends visual information to the brain.
   • The axons that run from the retina to the brain converge at the optic disk, a hole in the retina where the optic nerve fibres exit at the eye.
   • Cones are specialized visual receptors that play a key role in daylight vision and color vision
   • The fovea is a tiny spot in the centre of the retina that contains only cones; visual acuity is greatest at this spot
   • Rods are specialized visual receptors that play a key role in night vision and peripheral vision
   • Dark adaption is the process in which the eyes become more sensitive to light in low illumination
   • Light adaptation is the process whereby the eyes become less sensitive to light in high illumination
   • The receptive field of a visual cell is the retinal area that, when stimulated, affects the firing of that cell
   • Lateral antagonism occurs when neural activity in a cell opposes activity in surrounding cells
   • The optic chiasm is the point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain. This ensures that signals from both eyes go to both hemispheres of the brain.
   • Parallel processing involves simultaneously extracting different kinds of information from the same input
   • Feature detectors are neutrons that respond selectively to very specific features of more complex stimuli
   • Subtractive color mixing works by removing some wavelengths of light, leaving less light than was originally there.
   • Additive color mixing works by superimposing lights, putting more light in the mixture than exists in any one light by itself
   • The trichromatic theory of color vision holds that the human eye has 3 types of receptors with differing sensitivities to different light wavelengths
   • Color-blindless is rarely totally color blindness,, most colour-blind people are dichromats which means they can make do with only 2-color channels
   • Reversible figure is a drawing that is compatible with 2 interpretations that can shift back and forth
   • Perceptual set is a readiness to perceive a stimulus in a particular way.
   • Feature analysis is the process of detecting specific elements in visual input and assembling them into a more complex form.
   • Binocular depth cues are clues about distance based on the differing views of the 2 eyes
   • Monocular depth cues are clues about distance based on the image in either eye alone

3. The Auditory System

   • Humans can hear sounds ranging from a low of 20Hz up to a high of 20 000Hz
   • Sound is conducted differently in each section of the ear. The external ear depends on the vibration of air molecules. The middle ear depends on the vibration of moveable bones. The inner ear depends on waves in a fluid.
   • The external ear consists mainly of the pinna, sound-collecting cone. Sounds waves collected by the pinna are funnelled along the auditory canal toward the eardrum, a taut membrane that vibrates in response.
   • The middle ear consists of the ossicles that form a 3-stage lever system that converts relatively large movements with little force into smaller motions with greater force. The ossicles serve to amplify tiny changes in air pressure.
   • The inner ear consists of the cochlea, a fluid filled, coiled tunnel that contains the receptors for hearing. Sound enters the cochlea through the oval window, which is vibrated by the ossicles. The basilar membrane which runs the length of the spiralled cochlea, holds the auditory receptors. The auditory receptors are called hair cells.
   • Place theory holds the perception of pitch corresponds to the vibration of different portions, or places, along the basilar membrane.
   • Frequency theory holds that perception of pitch corresponds to the rate, or frequency, at which the entire basilar membrane vibrates.
   • Auditory localization is locating the source of a sound in space

4. Taste & Smell

   • The gustatory system is the sensory system for taste. The olfactory system is the sensory system for smell.
   • The gustatory receptors are clusters of taste cells found in the taste buds that line the trenches around tiny bumps on the tongue.
   • There are 4 primary tastes: sour, sweet, bitter, and salty.
   • Taste signals are routed through the thalamus and onto the insular cortex in the frontal lobe.
   • Taste cells respond to more than one taste, but they're more sensitive to one usually. Babies naturally like sweet and don't like sour, bitter, or salty. That is considered innate (hereditary). But more taste preferences are learned.
   • Supertasters have 4 times more taste buds than nontasters. Women are more likely to be super tasters than men. Smell contributes to our sense of taste as well.
   • Physical stimuli of the olfactory system are chemical senses dissolved in the mucous in the nose.
   • Receptors for smell are called olfactory cilia, hair like structures in the upper portion of the nasal passages
   • The receptors are routed through the prefrontal cortex rather than the thalamus
   • Pheromones are chemical messages that can be sent by one species to another (usually because of sexual attraction or aggression)

5. Touch

   • Pressure, pain and temperature are all things we can sense due to nerve endings in our skin.
   • We have nerve fibres that send messages from the environment to the spinal cord then to the brain stem where they cross to the other side of the brain.
   • Tactile signals are sent through the thalamus to the somatosensory cortex in the parietal lobe
   • Sensing pain is important so that we learn not to do certain actions to keep us from hurting ourselves
   • One way pain messages are sent to the brain it the fast pathway that uses myelinated neurons and registers localized pain in a fraction of a second.
   • The second way is the slow pathway that uses unmyelinated neurons and notifies us about less localized pain, longer lasting aches and burning pain that comes later
   • Gate control theory states that incoming pain sensations pass through a process in the spinal cord that functions as a gate which can be closed by skin receptor signals or brain receptor signals.

6. The Kinesthetic System

   • This monitors the positions of the various parts of the body .
   • Some of the receptors are in the joints and this system uses the same pathway as pressure/tactile stimulation.

7. The Vestibular System

   • This responds to gravity and keeps us informed of our bodys location in space.
   • Balance and equilibrium are provided by this system
   • Receptors for this system are in the semicircular canals in the inner ear

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