The Five (?) Senses

What a “Sense” Is Sensory Receptors detect some stimulus in the world Objective sensual data: waves of energy, vibrations, chemicals, pressure Associated brain areas interpret and reconstruct that information (perception) Interpretation is based on subjective elements Perceived information is then integrated into a holistic “experience”

So in other words: 1. Objective information is detected by sensory receptors, converted into neural impulses via transduction 2. Those impulses are filtered, interpreted, and integrated into our conscious experience based on what we know, anticipate, expect, or desire Objective data points are converted into a single subjective experience

Sensation The detection of a stimulus Occurs in the Sensory Receptors Dependent on whether the stimulus is above the Absolute Threshold Detectable 50% of the time on average Sensory Adaptation or “habituation” is the gradual decline in sensitivity to a stimulus Receptors “tire” and stop responding to chronic stimuli

Perception Occurs in the Brain Sorts information based on importance, frequency, etc. Conscious vs. Unconscious (subliminal) perception

The Senses: Vision Objective data are waves of radiation; light waves Reflected off of surfaces and detected by the rods and cones (sensory receptors) Limited range: the Visible Light Spectrum Different wavelengths correspond to colors Infrared and ultraviolet – just beyond the VLS

Anatomy of the Eye

Anatomy of the Eye Cornea – the clear “bulge” directly over the pupil/iris Iris – contracts or dilates to allow in the correct amount of light (the opening is the pupil) Lens – thickens or bends (accommodates) to focus light on the retina Near and far-sightedness are the result of improper focusing by the lens Retina – contains rods and cones

The Retina Contains rods and cones The Fovea The Blind Spot More rods than cones The Fovea Concentration of cones The Blind Spot Optic nerve exit; no rods/cones

Rods and Cones Rods are concentrated in the periphery of the visual field Sensitive to motion, light/dark contrast Cones are concentrated in the middle of the visual field Sensitive to detail, color Concentrated around the fovea, where light is generally focused Look directly at something to see detail

Visual Processing Begins when stimulated rods and cones send a neural signal (transduction) through bipolar cells to the ganglion cells One ganglion cell for each “visual field;” higher ratio of ganglion cells for cones than for rods Information from 10,000 cones becomes one neural signal Ganglion cells “perceive” – most important information from that field

Ganglion Cells The first step in perception Actually cells from the cortex; capable of analysis and sorting Reduce “noise” by limiting the number of signals The primary visual cortex receives only important information GC → Optic Nerve → Optic Chiasm → PVC

Color Vision Color is the way we perceive different wavelengths of light Objects do not have “color” objectively speaking Color vision is subjective, dependent on (1) the operation of the cones and (2) cultural considerations such as language Color has three “qualities

Hue Hue is what we generally mean by the word “color” Refers to the wavelength associated with that particular light

Saturation and Brightness Saturation is the color's “purity” Brightness is its perceived “intensity”

Theories of Color Vision Tri-Chromatic Theory Cones are either red, blue, or green sensitive Other colors are perceived when two or more different conical groups are stimulated (i.e., yellow is red and green both being stimulated) Explains deficits in color vision such as colorblindness

Colorblindness The inability to distinguish between certain colors Results from a lack of either red or green cones i.e., no green cones, so red and green wavelengths trigger only red

What do you see?

How about now?

This one?

Another Theory Opponent-Process Theory Rods and Cones work in opposing pairs When one is active, the other is inhibited When an active member stops, the opposing member is temporarily active red/green, blue/yellow, light/dark, motion (rods)

Afterimages Stare at the flag for 30 seconds, and then close your eyes What do you see?

Try This One Black and white contrast activates rods When you look away or close your eyes, the opponent rods become active, reversing the contrast

Visual Perception: Gestalt Principles Lead to the perception of unified wholes Perceptual constancy – even though aspects of an object change, perception of the whole does not Perceptual grouping rules – govern how objects fit together

Perceptual Grouping Proximity Closure Similarity Continuation Symmetry Simplicity Common Fate

Depth Perception Monocular Depth Cues: Linear perspective Texture gradient Familiar size Interposition

Binocular Cues Retinal Disparity Difference in time between signals gives the sensation of depth Pencil trick

Motion Perception Rods also sense the speed and directionality of motion Opponent-Processes create strange effects when opponent rods are activated like this and THIS!

The Senses: Audition Sensing and perceiving sounds Objective data are vibrations or “sound waves” Sensory receptors are located in the ears: hair cells Processing is done in the primary auditory cortex of the temporal lobe

Qualities of Sound Amplitude (loudness) – Dbs Pitch (frequency) – vibrations per second (hertz) Timbre (color) – overtones and harmonics, rather than pure tones

The Outer Ear Sound waves are collected by the Pinna, and then directed to the ear canal Sound travels through the ear canal to the ear drum

The Middle Ear The ear drum transfers vibrations to the ossicles Hammer (malleus), anvil (incus), stirrup (stapes) Amplify sound, transmit to oval window

The Inner Ear Oval window transfers vibrations to the cochlea Contains the basilar membrane, which contains hair cells Hair cells bend, creating nerve impulses

Deafness Conduction Deafness Nerve Deafness Damage to ossicles or other amplification agents Can be treated with amplifiers (hearing aids) Nerve Deafness Damage to the hair cells themselves Permanent – requires cochlear implants

Chemical Senses: Taste and Smell Objective data are chemicals Olfaction (smell) and gustation (taste) Linked together Direct, physical contact with the thing sensed

Olfaction Molecules in the air come in contact with olfactory receptors in the nasal cavity Each chemical stimulates a pattern of nerves Impulse sent to olfactory bulb

Olfaction Neural impulses are sent to the olfactory bulb, and then the temporal lobe and limbic system Bypasses the thalamus Smells are closely linked to emotions and memories Memory for smells tends to persist longer than other memories

Gustation Sense receptors are taste buds Specialized for sweet, salty, sour, bitter, and umami “taste” is weak; requires cooperation from smell

The Fifth Sense: Touch Pacinian corpuscles measure pressure Differences in gradation stimulate different nerves, creating the perception of texture

The Sixth Sense (?): Temperature Thermoreceptors detect heat Respond to changes in skin surface temperature

The Seventh Sense: Pain Nocireceptors respond to damage, stress A-delta fibers transmit fast, sharp pain C fibers transmit slow, dull pain

Pain Perception Pain is the “unpleasant” sensation associated with damage or injury Modulated by psychological factors The Gate-Control Theory Pain can be modulated by sending signals to “close” the “gates” that allow pain signals through Accomplished by rubbing the affected area Works for dull pain

Senses 8 and 9 – The Body Senses The Kinesthetic Sense – body location and posture Proprioreceptors in muscles and joints track information about location, muscle tone, movement The Vestibular Sense – balance Crystals in the semicircular canals of the inner ear shift as orientation changes Infection, illness, or sudden changes in air pressure can cause dizziness or vertigo