Sensation & Perception
Definition (#f7aeae)
Important (#edcae9)
Extra (#fffe9d)
KEY CONCEPTS:
Sensory Processing.
Vision.
Hearing.
Other Senses.
Perceptual Processes.
Bottom-Up vs. Top-Down.
Gestalt Principles
SENSORY PROCESSING:
Psychophysics: Study of relationships between physical stimuli and the sensations they evoke in a human observer; how information is processed.
The senses transduce physical energy into neural signals, that are sent back to the brain for further processing.
Transducer: Device that converts one kind of energy into another; ex: microphones/speakers (organs as biological transducers).
Sensations: Neural information detection at the brain from inputs from the sensory organs (eye, ear).
Humans lack specific transducers; ex: bioelectric fields of living creatures as detected by sharks.
Humans also only transduce specific ranges of energy e.g. bat’s pitch.
Making Sense of Our Senses:
Data Reduction System: Selecting and analysing only most important data to code & sent to the brain.
Ex: You are paying attention to the lecture & may not notice the feeling of your feet on the ground, or hear the noise from the air-conditioning.
Selection: Consciously only registering some senses and filter out many others happening.
Sensory adaptation: Change in sensory receptor responsiveness towards unchanging stimuli e.g. pressure from wearing watch.
Feature detection: Helps to also reduce sensory input by which the senses divide the world into important perceptual features e.g. lines, shapes, colours.
Perceptual features: Basic stimulus patterns.
Absolute threshold: Minimum amount of physical energy necessary to produce a sensation 50% of the time.
Difference threshold: The minimal difference between two stimuli required before the two stimuli can be coded as different 50% of the time.
Weber’s Law: Principle that two stimuli must differ by a minimum percentage to be perceived as different; depends on intensity too.
Unmaking of senses:
Subliminal Perception:
Stimuli with very low intensity, very brief or vague.
Used in advertisement, political campaigns to suggest or influence.
Synaesthesia:
One sense induces experience in another senses; ex: sense colours/music when tasting food.
Phantom Limb:
Experiencing sensations in a limb that does not exist.
Occurs among amputees – phantom sensations
ExtraSensory Perception (ESP):
Perception in absence of concrete sensory input.
Some term is as paranormal activity.
Clairvoyance – perceiving beyond our senses.
The Visual Stimulus (EYE):
Light: A form of electromagnetic radiation that is detected by the eye.
Wavelength: Determines the nature of light i.e. hue or color. As an example, red light has a different wavelength as compared to blue light.
Amplitude: Tells us the intensity or brightness of light.
Structure of the Eye:
Sclera:
White, outer part of eye.
Provides a protective layer for the eye, protecting it from damage.
Helps maintain shape & consists of multiple layers [episclera (external layer), stroma (middle layer), & endothelium (innermost layer)].
Iris:
Coloured circular muscle that controls entering amount of light that reaches the retina by contracting or dilating the pupil.
Pupil:
Opening in center of iris, it regulates the amount of light entering the eye.
Crucial for clear vision and for focusing on objects at different distances.
Size controlled by muscles in iris.
Cornea:
Transparent, dome-shaped part of the eye that covers the iris and pupil, allowing light to enter.
Bends light inward to help focus it into the retina.
Protects internal structure of the eye from damage.
Lens:
Transparent, somewhat flexible, disk-like structure – further bending light onto retina.
Ciliary muscles help alter the shape of lens for this purpose.
Retina:
Multilayered, light-sensitive surface at back of eye, containing photoreceptors.
Converts visual stimuli to neural impulses.
Light detection: Contains specialized cells called photoreceptors that are responsible for detecting light and converting it into electrical signals.
Vision: Essential for central and peripheral vision.
Visual Receptor Cells (Photoreceptors):
Cells on retina which convert electromagnetic energy into electrochemical impulses.
Rods:
Type of photoreceptor that are highly sensitive to light and responsible for night vision and peripheral vision. (12 million)
Only produce black and white.
Function well under low illumination.
Cones:
Responsible for color vision and sharp, detailed vision, particularly in bright light. (5 million)
Require more light than rods.
Fovea:
A specialized area within the retina densely packed with cone photoreceptors, responsible for high-acuity vision.
Tiny area in center of retina at which vision is best.
Highly dense with cones (around 50,000); rods absent.
Blind spot:
Region in the visual field where no light detection occurs because it lacks photoreceptor cells.
Place on retina containing neither rods or cones.
Where optic nerve leaves eye.
Color Vision Theories:
A condition where a person either lacks cones, or has cones that do not function normally.
Total colour-blindness is rare vs colour-weakness.
Commonly relating to red-green color blindness
Trichromatic theory:
Colour vision based on three “systems”: red vs green, blue vs yellow, black vs white.
Other colours are produced by a combination of these.
Problem: There seem to be a fourth primary colour i.e. yellow.
Opponent-Process Theory of Color:
Color vision theory Holds that we have 3 types of cones of varying lengths; red, green and blue (sensitive to different wavelengths).
Exciting one color in a pair (red) blocks the excitation in the other member of the pair (green).
After Image Effect: Fatigue caused by one response, will produce an afterimage of the opposite color.
THE AUDIO STIMULUS (EAR):
Sounds: Vibrations/rhythmic movements of air molecules that are captured by the auditory system.
Structure of the Ear:
External (air conduction) vs Internal (fluid conduction).
Sound waves are channeled from external to inner ear, as they collide with the eardrum.
Middle ear ossicles or bones, begin to vibrate, serving also as a connection between eardrum & cochlea.
Inner ear receives the vibrations from the ossicles at the oval window.
Cochlea: Snail-shaped organ in the inner ear, filled with fluid & contains sensory receptors for hearing.
Fluid vibrations transmit within the cochlea, & its hair cells bend & brush against membranes that become transduced into electrical signals
Theories of Hearing:
Conductive Hearing Loss:
Transfer of vibrations from outer to inner ear weakens i.e. damage at eardrum or ossicles.
Could be overcome by hearing aid, which amplifies sounds waves making them louder & clearer.
Sensorineural Hearing Loss:
Damaged hair cells or the auditory nerves.
Exposure to noisy environment or loud music leaves you at risk of noise-induced hearing loss
Frequency Theory:
As pitch rises, nerve impulses of a corresponding frequency are fed into the auditory nerve.
Place theory:
Higher and lower tones excite specific areas of the cochlea.
Ex: Higher tones are registered strongly at the opening of the cochlea vs end of cochlea which responds more to lower tones
Chemical Senses:
Smell:
Smell: Detection of chemical molecules that are airborne.
Air carries chemicals, which flow through roughly 5 million nerve fibres located in the upper nasal passages.
Stimulated fibres create action potentials, sent to the brain.
Odorant molecules are “shaped” to that allows them to fit into specific corresponding receptors. Only odorants that fit a receptor, shall trigger a signal.
Humans carry genes for 1000 types of receptors, though only 400 are expressed.
Taste:
Taste: Detection of chemical molecules that are found in food.
5 basic taste sensations: sweet, salty, sour, bitter, and umami.
Taste buds are your taste receptors; action potential set off when food is dissolved by saliva & chewing.
Taste buds mostly found around the top edges of the tongue. However, some are located elsewhere, including under the tongue.
Stimulation of the central part of the tongue causes no taste sensation
Touch:
Generally referred to as body related senses.
Skin receptors detect sensations of pain, temperature & touch, each with its own specific receptors.
Free nerve endings alone can produce all five sensations.
Kinesthetic:
Information on movement (kinesthesia) and bodily position (proprioception).
Awareness of how our body parts are moving (sensory receptors in joints and muscles) and sense of bodily position.
Muscle memory; Ex: in playing sport & walking without looking at feet.
Vestibular:
Balance and orientation; semicircular canals (ear as an organ of balance and not just hearing).
Ex: Motion sickness or dizziness; senses from eyes & ears don’t match up (sensory conflict theory).
Perceptual Process:
How sensations are organized into meaningful patterns.
Perceptual constructions: Mental models of external events that are actively created by your brain.
Perceptual hypothesis: Initial plan or guess about how to actively guide our interpretation of sensations.
Illusions: A perceptual misconstruction - information that is sent to the brain from the senses is interpreted in a way that is not consistent with objective reality
Bottom-Up or Top-Down Processing:
Perceptions typically constructing in a top-down, or bottom-up fashion.
Bottom-up processing: Analyzing information starting at the bottom (small units) and going upward (to the brain) to form a complete perception.
Top-down processing: Pre-existing knowledge & experience that is used to rapidly organize features into a whole without necessarily processing individual components.
Gestalt Principles of Organization:
Gestalt School of thought: The whole is greater than the sum of its parts.
Figure–ground organization: Inborn; part of a stimulus stands out as an object (figure) against a plain background (ground).
Reversible figure: figure and ground that can be reversed.
Nearness: stimuli that are near each other tend to be grouped together.
Similarity: stimuli that are similar in size, shape, color, or form tend to be grouped together.
Continuation/continuity: perceptions tend toward simplicity and continuity.
Closure: tendency to complete a figure so that it has a consistent overall form.
Common region: stimuli that are found within a common area tend to be seen as a group.
Proximity: Stimuli that are close together tend to be related than things spaced apart
Other Perceptual Phenomena:
Ambiguous stimuli: Patterns allowing more than one interpretation.
Size & Shape Constancy: Perceived size and shape remains constant despite changes in retinal image.
Brightness constancy: That the relative brightness of objects stays the same even as lighting conditions change.
Inattentional blindness: Failure to perceive a stimulus that is in plain view but not the focus of attention.
Relative size: If 2 objects of the same size appear at different distances, the distant object looks smaller.
Light and shadow: Most objects are lit in ways that create clear patterns of light and shadow, resulting in a three-dimensional appearance.
Overlap: When one object partially blocks another, it appears to be closer.
Perceptual habits: Ingrained patterns of organization and attention perceiving things as they usually are.