Sensation and Perception: An Overview

• Sensation is awareness resulting from the stimulation of a sense organ.
• Perception is the organization and interpretation of sensations.

Introduction

• The ability to detect and interpret events allows us to respond to stimuli appropriately.
• Sensation and perception work together to allow us to experience the world through the sense organs.
• The sense organs include eyes (sight), ears (hearing), nose (smelling), tongue (tasting), and skin (feeling).
• This helps us combine current learning from the environment with prior knowledge to make judgments and appropriate behaviors.
• This knowledge helps experts in defense, military, clinical, health, and sports fields.
• Research in this area helps us understand and prepare people to cope with diverse events like driving, flying, and robotics.

Sensation

• A sense is a system comprising sensory cell types responding to a specific physical phenomenon.
• It also involves a region of the brain where signals are received and interpreted.
• Senses, their operation, classification, and theories are studied across neuroscience, cognitive science, and philosophy of perception.
• The nervous system dedicates a system or organ to each sense.
• A wide variety of stimuli inform and guide behaviors, always involving interpretation.
• We experience stimuli as created by our senses, not directly.
• Senses are divided into exteroceptive and interoceptive categories.
• Exteroceptive senses perceive the body's position, motion, and state, also known as proprioceptive senses.
• The six senses are seeing, hearing, smelling, touching, tasting and proprioception (monitoring body positions).
• Each sense involves transduction: converting detected stimuli into electrical impulses sent to the brain.
• Interoception is the process by which the nervous system senses and integrates information about the inner state of the body.
• It covers both conscious and non-conscious levels of information processing.
• Interoception includes physiological systems critical to body regulation, maintenance of homeostasis and survival.

Measuring Sensation: Sensory Thresholds

• Psychophysics studies the effects of physical stimuli on sensory perceptions and mental states.
• Gustav Fechner (1801-1887) founded psychophysics to study the relationship between stimulus strength and detection ability.
• Eyes detect light, ears detect sound, skin senses pressure/temp, tongues react to food molecules, and noses detect scents.
• Fechner's techniques were designed to determine the limits of human sensation and detect faint stimuli which is known as the absolute threshold.
• For example, a teaspoon of sugar in 2 gallons of water can be tasted and one drop of perfume can be smelled in a three-room apartment.
• The absolute threshold is the intensity of a stimulus that allows an organism to just barely detect it.
• Psychophysics experiments present individuals with trials where a signal is sometimes present.
• Two stimuli can also be presented that are either the same or different.
• Signal detection analysis analyzes responses to separate true signals from background noise using hearing test results.

Signal Detection Analysis

• A psychophysics experiment yields two measures: sensitivity and response bias.
• Sensitivity refers to the true ability to detect the presence or absence of signals.
• Higher hearing ability leads to higher sensitivity.
• Response bias is the tendency to respond "yes" to trials irrespective of sensitivity.
• A soldier on guard duty who is detecting faint sounds of breaking branches requires a sensitive ear.
• A false alarm can be less costly than a miss and so a lenient response bias is adopted.

Just Noticeable Difference

• An important criterion concerning the ability to assess differences between stimuli which is known as the Just Noticeable Difference (JND).
• The difference threshold (or just noticeable difference) is the change in a stimulus that can just be detected by the organism.
• Ernst Weber (1795-1878) discovered that the ability to detect differences depends not on the difference size.
• The ability depends on the size of the difference relative to the absolute stimulus size.
• Weber's law maintains that the JND is a constant proportion of the original intensity.

The Senses - Sight

• Vision occurs when light enters the eye through the cornea which protects that eye and focuses the incoming light.
• Light passes through the pupil, a small opening in the center of the eye.
• The iris, controls the pupil size by constricting or dilating in response to light intensity.
• In dark theaters, muscles in the iris open the pupil to allow more light.
• Complete adaptation may take up to 20 minutes.
• Behind the pupil is the lens, focusing incoming light on the retina.
• The retina is a layer of tissue at the back of the eye that contains photoreceptor cells.
• Visual accommodation occurs as eyes move from near to distant objects.
• Accommodation is the process of changing the curvature of the lens to keep light focused on the retina.
• Rays from the top of an image strike the bottom of the retina and vice versa, causing the image to be inverted.
• The projected retinal image is flat, however, our final perception is three-dimensional.
• Accommodation is not always perfect leading to normal, nearsighted, and farsighted eyes.
• Nearsightedness occurs when the focus is in front of the retina.
• Farsightedness occurs when the focus is behind the retina.
• Eyeglasses and contact lenses are used to correct these problems by adding another lens.
• Laser eye surgery corrects the problem by reshaping the eye's own lens.
• The retina contains layers of neurons that respond to light, known as rods and cones and activates these cells.
• Rods are visual neurons specialized in detecting black, white, and grey colors.
• There are about 120 million rods in each eye but do not provide great detail.
• Rods are highly sensitive to shorter-waved (darker) and weak light, helping us see in dim light, especially at night.
• Rods are located primarily around the edges of the retina, and therefore are particularly active in peripheral vision.
• Cones are visual neurons specialized in detecting fine details and colors.
• About 5 million cones in each eye enable color vision and operate best in bright light.
• Cones are located primarily in and around the fovea, the retina's central point.
• Sensory information from the retina relays through the thalamus to corresponding areas in the visual cortex.
• The visual cortex is located in the occipital lobe.

Hearing (Audition)

• The ear detects sound waves which is similar to how the eye detects light waves.
• Vibrating objects cause air molecules to bump into each produce sound waves.
• The sound waves travel from their source as peaks and valleys like ripples from a stone tossed into a pond.
• Sound waves are carried within mediums unlike light waves which can travel in a vacuum.
• The changes in pressure associated with these mediums is how the ear detects waves.
• The wavelength of the sound wave (frequency) is measured in terms of waves per second determining pitch.
• Longer sound waves have lower frequency and produce a lower pitch.
• Shorter waves have higher frequency and higher pitch.
• Height of the sound wave (amplitude) determines the amount of energy containing and is perceived as loudness.
• Larger waves are perceived as louder.
• Loudness is measured using the unit of relative loudness known as the decibel.
• Zero decibels represent the absolute threshold for human hearing, below we can not hear sound.
• Increase in 10 decibels represents a tenfold increase in loudness.
• Conversation is 1,000 times louder than a faint whisper.
• Jackhammer is 10 billion times louder than a whisper.
• Audition begins in pinna.
• The external and visible part of the ear is shaped like a funnel to draw in sound waves and auditory canal.
• Sound waves strike the eardrum, which vibrates with the waves.
• Resulting vibrations are relayed into the middle ear through three tiny bones; hammer, anvil, and stirrup.
• The vibrations cause the oval window to vibrate.
• This disturbs the fluid inside the cochlea containing about 16,000 hair cells, each holding a bundle of fibers (cilia) on tip.
• The cilia are sensitive and can detect movement.
• Movements of the fluid in the cochlea bend the hair cells.
• This triggers nerve impulses which are sent to auditory cortex.

Theories of Hearing: Place and Frequency

• Frequency theory of hearing proposes that nerve impulses of corresponding frequency will be sent to the auditory nerve.
• High-pitched sounds theory has problem, neurons cannot fire fast enough.
• To reach speed, neurons work together in volley system.
• Cochlea relays information about place activated by sound.
• Place theory of hearing proposes different areas of the cochlea, responding to different frequencies.
• High and low tones excite areas near opening/tip of cochlea.
• Pitch is determined by which areas are firing most frequently.
• Cars placed on sides of head enable us to benefit from stereophonic hearing.
• Ears receives sound with intensity/sooneness.
• Intensity and speed differences detected.
• Sound is equidistant from both ears.
• Harder to pinpoint; dogs (and people) tends to cock heads.
• Conductive hearing loss can be caused by physical damage to the ear.
• This can result in a reduced ability transfer vibrations from the outer ear to the inner ear.
• Sensorineural hearing loss is caused by damage to the cilia or to the auditory nerve.

Tasting

• Taste begins the taste receptors on the tongue.
• Tongue detects six different taste sensations which includes Umami, Sweet, salty, sour, bitter, and piquancy.
• Umami is a meaty taste that is associated with soy, seaweed and mushrooms.
• It is particularly found in monosodium glutamate (MSG), a popular flavor enhancer.
• Chewing food allows it to dissolve and enter the taste buds, triggering the nerve impulses transmitted to the brain.
• Human tongues covered in 2000 to 10000 tastebuds.
• Taste occurs when they are activated and transmit a neural impulse
• Tastebud lives for five days and New tastebuds can take their place.
• The rate of creation decreases making us less sensitive to taste.
• Helps explain why foods more enjoyable for adults.
• Sensory cortex area responding to taste similar location as smell leading to combined taste and smell experience.

Smelling or Olfaction

• Airborne chemical molecules inhaled are detected by 10 to 20 million receptor cells embedded in olfactory membrane passage.
• Olfactory receptor cells topped with tentacle-like protrusions containing receptor proteins.
• Odor receptor stimulates membrane, membrane sends neural messages up olfactory nerve to brain
• Odor receptor cell types are estimated that we can
• Receptors come in many different shapes and respond selectively to different smells.
• Theory says different chemical molecules fit to receptor cells so odors are detected according to influence on combination
• Sense of smell peaks in early adulthood and then begins slow decline.
• After age of 60 and 70, sense of smell has diminished

Touch

• Touch is essential to human development.
• Infants are thrive when cuddled and attended to which communicates warmth, caring and support.
• Touch is important for social Interactions.
• Sensory organ for touch is skin/largest organ containing nerve endings responding to types of pressure/temperature.
• When you touch parts of body, areas are more ticklish.
• Nerve endings/skin respond to basic sensations.
• Pressure, hot, cold, pain which create other sensations.
• Sensitivity is created by specialised receptors.
• Skin provides information about touch and temperature.
• Skin provides proprioception with specialised neurons sending messages/bone throughout body.
• The ability to track body movements is provided by the vestibular system and provides liquid filled balances in maintaining bodily balance.