Introduction to Sensation and Perception

Sensation and Perception

• Sensation is the process where sensory systems detect raw information and convert it into neural activity.
• Perception is the process where the brain interprets sensory information.

Bottom-Up vs. Top-Down Processing

• Bottom-up processing starts with sensory receptors and works its way up to complex interpretations.
• Top-down processing is driven by our existing knowledge, experiences, and expectations.

Sensory Receptors

• Sensory receptors are specialized cells that receive and convert sensory stimuli into neural signals.
• Examples of sensory stimuli include light, sound, touch, temperature, taste, and smell.
• The process of converting sensory signals into electrical signals that the brain can understand is called transduction.

The Five Senses

• Sight, hearing, touch, smell, and taste.

Psychophysics

• The study of how physical stimuli affect our senses and perceptions.
• Absolute threshold is the minimum stimulation needed to detect a stimulus 50% of the time.
• Signal Detection Theory predicts how and when a person will detect a weak stimulus.
  • Sensitivity is the true ability of an individual to detect signals.
  • Response Bias is a behavioural tendency to respond "yes" to trials and will vary from person to person and is independent of sensitivity
• Weber's Law indicates that the ability to detect a difference in stimulus intensity depends on the initial intensity of the stimulus.

Vision

• Vision is the process of detecting and interpreting electromagnetic energy.
• The visible light spectrum is a narrow band of electromagnetic radiation.
• The eye detects visual information using various components like the cornea, pupil, iris, lens, and retina.
• The retina contains photoreceptors (rods and cones).
• Rods are more sensitive to light and work in dim light conditions, while cones detect colors and are concentrated in the fovea.
• The optic nerve carries information from the retina to the brain.
• The blind spot is the point where the optic nerve leaves the eye.

Eye Anatomy

• The eye is a complex structure with many parts, each playing a role in vision.
  • Sclera, Cornea, Iris, Pupil, Lens, Ciliary body, Choroid, Retina, Fovea centralis, Optic disc, Blood vessels, Optic nerve, Suspensory ligament, Aqueous body, Vitreous body.

Visual Pathways / Streams

• Visual information travels through two major pathways after being processed in the occipital lobe
  • Dorsal stream information travels to the parietal lobe (how/where) for spatial reasoning
    • involved in guiding our action and movements in the world
  • Ventral stream information is sent to the temporal lobe (what/recognition)
  • important for object identification

Visual Accommodation

• The process where the eye changes the shape of the lens to keep an image focused on the retina when an object is close up or far away.
  • Myopia (nearsighted) - image is focused in front of the retina
  • Hyperopia (farsighted) - image is focused behind the retina

Optic Nerves

• Millions of ganglion neurons make up the optic nerve; sending vast amounts of visual information to the brain via the thalamus.
• The retina and optic nerve act as active processors and analyzers of visual information.

Perceiving Colors

• Hue is the dimension of color, determined by the wavelength of light.
• Young-Helmholtz Trichromatic Theory proposes that color perception is determined by the activation of three types of cones, sensitive to different wavelengths.
• Opponent-Process Theory suggests that we perceive color based on opposing color pairs. These include: red-green, yellow-blue, and black-white.
• Color blindness is the inability to detect certain colors due to a deficiency in a type of cone or retinal ganglion cells.

Perceiving Form

• Gestalt Psychology is the idea that the whole is greater than the sum of its parts; meaning we tend to perceive things as whole pieces rather than individual elements.
• Principles like figure-ground, proximity, similarity, continuity, and closure influence how we organize visual information.

Perceiving Depth

• Depth perception is the ability to perceive three-dimensional space and judge distance.
• Binocular depth cues require the coordination of both eyes for depth perception. (retinal image disparity, convergence)
• Monocular depth cues allow for depth perception when one eye is used. (examples include linear perspective, relative size, interposition, texture gradient, height in visual field )

Perceiving Motion

• Beta effect: Perception of motion when sequentially presented with different images next to each other over time
• Phi phenomenon: Perception of motion caused by the alternation between objects appearing and disappearing

Audition

• The ability to detect and interpret sound.
• Hearing involves the detection of sound waves and their interpretation in the brain.

Hearing

• Frequency is the number of sound cycles per second; measured in Hertz (Hz)
• Amplitude is the height or strength of the sound waves which indicates energy carried in sound and its loudness; measured in decibels (dB)

Ear Anatomy

• Pinna, Ear Canal, Tympanic membrane (eardrum), Ossicles (malleus, incus, stapes), Oval window, Cochlea, Semicircular canals, Auditory nerve

Anatomy of the Auditory System

• Outer ear (pinna, auditory canal, eardrum) collects and transmits sound waves.
• Middle ear (ossicles) amplifies vibrations.
• Inner ear (cochlea) converts vibrations to electrical signals.

Theories of Hearing

• Temporal theory: Frequency of a tone is represented by the firing rate of nerve fibres that respond to that sound.
• Place theory: States that different areas on the basilar membrane respond to different frequencies of sound based on stimulation.
• Both theories work in combination, different frequencies use both place and temporal theories for perception

Sound Localization

• How we perceive sound patterns to discern the direction and distance different sources of sound are located
  • monaural cues (based on information on a single ear)
  • binaural cues (require the use of two ears); important for localizing sounds in the horizontal plane - interaural level difference (ILD), interaural timing difference (ITD)

Hearing Problems

• Conductive hearing loss is due to a problem with the vibration of the eardrum or ossicles.
• Sensorineural hearing loss is due to a failure to transmit neural signals from the cochlea to the brain.

Gustation

• The sense of taste is one of the five senses.
• Taste buds on the tongue detect five basic tastes: sweet, salty, sour, bitter, and umami.
• These tastes send signals to the brain, enabling us to experience flavors.

Anatomy of the Tongue

• Taste pores are tiny openings on the tongue's surface; allowing food and beverage molecules to interact with sensory cells within taste buds
• Taste receptor cells respond to different taste qualities and send signals to brain to trigger sensation of tastes.
• Tongue surfaces contain taste buds located within papillae, small structures.

Olfaction

• Smelling is the sense of smell.
• It involves chemoreceptors in the nose that detect volatile gaseous odorants and they translate them into neural signals for the brain to interpret.

Physiology of Olfaction

• Nasal cavity contains a thin film of mucous to dissolve odors.
• Olfactory neurons with cilia (hair-like projections) detect the odor.
• Smell signals go from the olfactory bulb (via Cranial nerve I) to parts of the brain (frontal and temporal lobes) to process.

Pheromones

• Chemical messages sent by another individual; ectohormones.
• Often associated with behavioral changes in another animal, communicate about reproductive status of a potential mate.
• Function: signaling food, alarming other animals, defending territory, signalling bond between mother and offspring.

Somatosensory

• The somatosensory system involves the input of conscious perception of touch, pressure, pain, temperature, position, and vibration.
• Four distinct skin sensations: pressure, warmth, cold, and pain.
• Various sensory receptors in the skin and muscles detect touch, pressure, pain, and temperature (examples include: Meissner's Corpuscle, Merkel's Disc, Pacinian Corpuscle, Ruffini's Ending.
• Specific receptors help sense a change in stimuli.

Case Studies

• Examples of different sensory systems that are important in humans and animal development. (examples include:
  • Harlow's Monkey study (comfort and emotional security)
  • Physical injuries causing anosmia (partial/complete loss sense of smell)

Other Sensory Systems

• Vestibular input: Sense of balance located in the inner ear.
• Proprioceptive input: How muscles, tendons, and ligaments help sense body position and movements; location in space.
• Interoceptive input: hidden sense; perception of feedback internally such as; stomach grumbling or feeling sick

Perception

• Perception is an active process of interpreting sensory information to understand the world around us.
• The different types of perception - visual, auditory, olfactory, gustatory, tactile.

Sensory Interaction

• How different senses interact; McGurk effect.

Selective Attention

• Cognitive processes focus on one specific piece of information/task while ignoring other irrelevant parts of the environment.
• Helps prioritize and manage limited resources for better cognitive efficiency.
• Sensory adaptation is the ability to focus on relevant stimuli.

Perceptual Constancy

• The ability to recognize objects as stable despite changes in input such as lighting, distance, or angle
• Sensory adaptation is important for perceptual stability

Illusions

• Different types of illusions caused by misinterpretations of sensory inputs.
  • Visual Illusions (examples include: Müller-Lyer illusion, Ames room illusion)
  • Auditory Illusions (examples include Shepard Tone, McGurk effect)
  • Tactile Illusions (examples include: Feeling ownership of a fake hand when it is stroked with your hidden real hand, Phantom limb sensation, misinterpreting taste or smell from interactions with other senses)
  • Cognitive Illusions (examples include Stroop effect, Moon illusion)

Factors Affecting Perception

• Sensory adaptation
• Sensory deprivation
• Selective attention
• Motivation
• Beliefs, expectations, prejudices
• Life Experiences/Culture.

Gestalt Principles of Perception

• Field of psychology that emphasizes the idea that the whole is greater than the sum of its parts; understanding the mind is in how it perceives patterns and wholes. Examples include:
  • Figure-ground relationship
  • Proximity
  • Similarity
  • Continuity
  • Closure