Sensation and Perception

Principals of BehaviorChapter Three

Sensation

Sensation is the process by which we detect and process stimuli in the environment.

Sensation is the process by which we detect physical energy such as light, sound and heat from the environment by specialized sensory receptors and encoding it as neural signals.

Transduction

The process of transforming physical energy into neural signals via sensory signals.

Sensory receptors cells in one the sense organs ( eye) receive stimulus such as light. If the amount of stimuli, via the light is strong enough the receptor cell (neuron) fires sending a neural signal (action potential) to the appropriate area of the brain occipital lobe.

 

Psychophysics The field that studies links between the

physical properties of stimuli and a person’s experience of them.

Thresholds-as we are constantly bombarded with energy,( x-rays, radio waves, ultraviolet and infrared light) Our senses allow only a restricted awareness of this energy as in what stimuli we can detect.

This “restricted awareness” are called thresholds, and they are different for each sensory system.

Sensory Thresholds

Absolute threshold

Difference threshold

Just noticeable Difference

Subliminal Perception

The Visual System

Properties of Light Energy is the form of light wave Brightness-amplitude of the wave Saturation-purity of the wave (presence

of more than one wave is less pure or saturated)

Color-length of the wave.

The Structure of the Eye

Cornea-transparent protector through which light enters the eye. Curved surface bends the light to focus at the back of th eye

Pupil-a small adjustable opening that regulates the amount of light that enters the eye through a colored muscle called the iris.

Lens-transparent structure behind the pupil that also focuses The cornea does most of the bending, while the lens fine tunes the focus in process called accommodation.

accommodation –affects acuity which is the sharpness of our vision, which can be affected by small distortions in the shape of the eye.

The shape of the eye influences the focus of the image on the retina.

Accommodation

Farsightedness- lens is longer and flatter than normal and therefore unable to bring close objects into focus. Focusing the image behind the retina

Nearsightedness-- eyeball is shorter than normal, causing focus to later than normal and therefore objects up close appear blurred. Focusing the image in front of the retina.

Parts of the Eye

Retina-the light sensitive outer surface of the eye, containing the receptors that begin visual processing

receptor cells- located at the back of the retina and converts light into a neural signal Two types of receptor cells, rods and cones.

rods- located around the outside of the retina, responsible for black, white & gray vision, vision in dim light, and peripheral vision.

cones-located near the fovea, which was the central focal point in the retina, which is responsible for color, fine detail and vision in day light.

Photoreceptors

Receptor Cells (Rods & Cones)

Bipolar Cells

Ganglion Cells

Optic Nerve ( axons of Bipolar cells)

How the Eye Works Blind spot-is the point at which the

optic nerve leaves the eye and is called the blind spot because there are no receptors there.

Optic nerve-the bundle of axons that carries neural messages from each eye to the brain.

Optic chiasm-point near the base of the brain where some, not all of the optic nerve fibers split and cross to the other side of the brain.

Hemispheric projection:Visual fields

Theories of Color PerceptionTrichromatic Theory

Proposed three types of cones: red, blue, green

Different shades of color correspond to different amounts of light received by each of these three types of cones.

Cones fire message to the occipital lobe Combination of which cones are firing as

well as the rate of firing that determines the color perceived.

Problem: After image

Stare at the cross in center of the flag for 30 seconds, now stare at white wall or piece of

paper

Theories of Color Perception:

Opponent Process Four primary colors: red, green, blue, yellow Cones are arranged in pairs, red with green,

blue with yellow If one memory of the pair is stimulated, i.e.

red, the other member of the pair is turned off, i.e. green.

Afterimage-if a person stares at a red object too long, it weakens that members ability to inhibit the other cell. So, if staring at a red image for too long, one might begin to see green as an after-image.

Auditory Conduction

Stimulus is sound waves which consist of compressed and expanded air.

Sound wave-change in pressure caused when molecules of air collide with one another and then move apart again.

Properties of the sound waves:

Amplitude = loudness (height of the wave)

Frequency = pitch (length of the wave) longer-lower, shorter- higher. (Hz)

Structure of the Ear

Outer ear Pinna (Ear Flap) channels sound waves

through the auditory canal to the eardrum, which is a tight membrane that vibrates with the waves.

Middle Ear consists of three tiny bones

( ossicles),the hammer, anvil and stirrup which hit each each other in a sequence that carries the vibrations to the inner ear.

Inner Ear

Inner Ear Oval Window: Vibrations from the

stirrup on the oval window set up another chain reaction within the inner ear.

Cochlea: is a fluid filled a snail like structure to which the oval window is attached. Vibrations of the oval window cause the fluid of the cochlea to begin to vibrate.

Basilar membrane-membrane running through the middle of the cochlea.

Sound Conduction

Organ of Corti-rests on top of the basilar membrane.

contains receptor cells in the form of hair fibers.

Hair fibers bend in response to the vibrations which in turn causes the receptor cells to fire (action potential).

Sends a neural impulse to the auditory nerve which connects to the temporal lobe region of the brain.

 

Theories of Pitch Perception

Place theory-pitch perceived depends on the place where the hair cells were stimulated on the organ of corti ( High pitch corresponds to bending of hair cells closest to the oval window).

Frequency theory-pitch corresponds to the how fast the basilar membrane vibrates ( the higher the pitch, the faster the vibrations).

Volley Principle

Volley Principal-combination of both theories.

Place theory works for pitches above 1000 Hz.

Frequency theory works for pitch below 100 hz.

Volley-In between, say 300 hz, groups of neurons take turns sending the message to the brain, Group one, 100 hz, Group two, 100 hz, etc.

Hearing Impairments Conduction deafness damage to the

mechanical system that conducts sound to the cochlea. (punctured eardrum or damage to the small inner bones) Hearing aid could help by amplifying vibrations.

Nerve deafness damage to the hair cell receptors or associated nerves. Usually caused by disease or something else biological. cochlear implant can help restore hearing via an

electronic device that translates sounds into electrical signals, which are wired into the cochlea’s nerves, conveying some information about sound to the brain.

Touch Essential for Survival Deprivation of touch in animal and human

infants leads to failure to thrive and/or death.

Sense of touch is actually a mix of at least four distinct skin senses: -pressure, warmth, cold pain.

Pain

Pain is essential as it is the body’s way of telling you that something is wrong.

People who cannot feel pain die by early adult hood because they cannot tell when they have an infection or they are hurt .

Pain has a strong psychological component, not easily understood.

No theory of pain explains all the phenomenon. Many psychological influences on pain such as

distraction or endorphin release can modulate pain. (i.e athletes that continue to play while they are injured.)

Gate Control Theory Spinal cord contains a “ gate” that either blocks pain

signals or allows the signal to pass on to the brain. Gate can be closed by non-pain signals coming from

the body and by signals coming from the brain. “Gate” not a physical structure, represents a

relative balance in neural activity within the spinal cord.

Stimulation of the pain receptors releases substance P which activates neurons that open the spinal gates, resulting in a pain signal that is sent to the brain

Perception of Pain

Message sent from spinal cord to brain. Areas of the brain, influenced by

physiological and psychological factors, interprets the pain sensation that either opens the gates further increasing the pain, or closes the gates, thus dampening the pain.

The activity of the gate can be closed by signals coming from stimulation of competing signals from other skin sensations such as rubbing, which can reduce the feeling of pain.

Taste Chemical sense -involves four basic

sensations-sweet, sour, salty, and bitter. Taste buds, which are bumps on our

tongues, for each of the four basic taste sensations.

Taste buds contain a pore that catches food molecules.

Taste receptors are antenna like hairs the project into the pore that respond to one of the four sensations.

Taste receptors reproduce themselves every week or two although this diminishes with age.

Taste is enhanced by smell. Smell + taste = flavor.

Olfaction (Smell) Chemical Sense-most primitive Odors have power to evoke memories and

feelings due to a direct connection between olfaction and the limbic system.

Sense of smell is activated by a complex protein in the nasal gland called Oderant Binding Protein that binds with airborne molecules in the olfactory epithelium.

Olfactory receptors recognize odors individually, and respond selectively to different aromas.

Axon fibers of receptor cells go directly to the olfactory bulb, which in turn sends a message to the temporal lobe which records the awareness of smell.

Perception

Terms Perceptions- perceive the world

through our senses, however we transform meaningless sensations into meaningful perceptions.

Selective Attention-Our conscious attention is selective, therefore at any one moment we focus our awareness on only a limited aspect of all that we are capable of experiencing.

Cocktail Party Effect-the ability to attend selectively to only one voice among many

Perceptual Organization

Gestalt-given a cluster of sensations, the human perceiver organizes them into an organized whole.

Figure-ground- our first perceptual task is to perceive any object called the figure, distinct from its surroundings, called the ground. (i.e. words on paper).

Grouping- To bring order and form to these basic sensations, and our minds follow certain rules.

Grouping Rules Proximity- We group nearby figures

together. Similarity - Figures similar to each other

we group together. Continuity- We perceive smooth

continuous patterns rather than discontinuous ones.

Connectedness-When they are uniform and linked we perceive spots, lines or areas as a single unit.

Closure- the tendency to “fill in” gaps in a stimulus so that the image makes sense.

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Depth Perception Seeing objects in three dimension when

our retinal images are only two dimensional. This enables us to estimate their distance.

Monocular cues-distance cues, such as linear perspective and overlap, available to either eye alone.

Binocular cues-depth cues such as retinal disparity and convergence, that depend on the use of two eyes.

Monocular Cues

Interposition- If one object partially blocks our view of another we see it as closer.

Texture gradient-a gradual change from a coarse distinct texture to a fine indistinct texture signals increasing distance. Far objects appear smaller and more densely packed.

Linear perspective-parallel lines, such as railroad tracks, appear to converge with distance. The more the lines converge, their greater their perceived distance.

Light and Shadow- Nearby objects reflect more light to our eyes. Thus given two identical objects, the dimmer one seems farther away.

Binocular Cues

Because our eyes are about 2 ½ inches apart, our retina receive slightly different images of the world.

Retinal disparity- When the brain compares these two images, the difference between them is called retinal disparity and provides an important cue to the relative distance of different objects.

Motion Perception Our brain computes motion based

partly on its assumption that shrinking objects are retreating and enlarging objects are approaching.

Phi phenomenon-when two adjacent stationary lights blink on and off in quick succession, we perceive a single light moving back and forth between them

Visual Illusions

Illusions due to misleading cues in stimuli that give rise to inaccurate or impossible perceptions.

Escher Photos