Key Terms
Absolute Threshold- the minimum amount of stimulus energy that a person can detect

Apparent Movement- the perception that a stationary object is moving

Attention- the process of focusing awareness on a narrowed aspect of the environment

Auditory nerve- the nerve structure that receives information about sound from the hair cells of the inner ear and carries these neural impulses to the brain’s auditory areas

Binding- in the sense if vision, the bringing together and integration of what is processed by different neural pathways or cells

Binocular cues- depth cues that depend on the combination of the images in the left and right eyes and on the way the two eyes work together

Bottom/up processing- the operation in sensation and perception in which sensory receptors register information about the external environment and send it up to the brain for interpretation

Cones- the receptor cells in the retina that allow for color perception

Convergance- a binocular cue to depth and distance in which the muscle movements in our two eyes provide information about how deep and/or far away something is

Depth Perception- the ability to perceive objects in the 3-D

Difference Threshold- the degree of difference that must exist between two stimuli before the difference is detected

Feature Detectors- neurons in the brains visual system that respond to particular features of a stimulus

figure-ground relationships- the principle by which we organize the perceptional field into stimuli that stand out (figure) and those that are left over (ground)

frequency theory- theory of how the inner ear registers the frequency of a sound, stating that the perception of a sound’s frequency depends on how often the auditory nerve fires

gestalt psychology- a school of thought interested in how people naturally organize their perceptions according to certain patterns

inner ear- the part of the ear that includes the oval window, cochlea, and basilar membrane and who’s function is to convert sound waves into neural impulses and send them to the brain

kinesthetic sensors- senses that provide information about movement, posture, and orientation

middle ear- the part of the ear that channels sound through the ear drum, hammer, anvil, and stirrup to the inner ear

monocular cues- powerful depth cues available from the image in one eye, either the right or left

noise- irrelevant and competing stimuli-not only sounds but also any distracting stimuli for our senses

olfactory epithelium- the lining of the roof of the nasal cavity, containing a sheet of receptor cells for smell

opponent-process theory- theory stating that cells in the visual system respond to complimentary pairs of red-green and blue-yellow colors; a given cell might be excited by red and inhibited by green, whereas another cell may be excited by yellow and inhibited by blue

optic nerve- the structure at the back of the eye, made up of axions of the ganglion cells, that carries visual information to the rain for further processing

outer ear- the outermost part of the ear, consisting of the pinna and the external auditory canal

pain- the sensation that warns us damage to our bodies

papilae- rounded bumps above the tongues surface that contains taste buds, the receptors for taste

parallel processing- simultaneous distribution of information across different neural pathways

perception- the process of organizing and interpreting sensory information so that is has meaning

perceptual constancy- the recognition that objects our constant and unchanging even though sensory input about them is changing

perceptual set- a predisposition or readiness to perceive something in a particular way

place theory- theory on how the inner ear registers the frequency of sound, stating that each frequency produces vibrations at a particular spot on the basilar membrane

retina- the multilayered light-sensitive surface in the eye that records electromagnetic energy and converts it into neural impulses for processing in the brain

rods- the receptor cells in the retina that are sensitive to light but not very useful for color vision
Selective attention-the process of focusing on a specific aspect of experience while ignoring others
Semicircular canals- three fluid-filled circular tubes in the inner ear containing the sensory receptors that detect head motion cause when we tilted of move our head and/or body
Sensation-the process of receiving stimulus energies from the external environment and transforming those energies into neural energy
Sensory adaptation- a change in the responsiveness of the sensory system based on the average level of surrounding stimulation
Sensory receptor- specialized cells that can detect stimulus information and transmit it to sensory (afferent) nerves and the brain.
Signal detection theory- a theory of perception that focuses on decision making about stimuli in the presence of uncertainty
Subliminal perception – the detection of information below the level of conscious awareness
Thermorecptors - sensory nerve receptors under the skin that respond to changes in temperature at or near the skin and provide input to keep the body temperature at 98 degrees Fahrenheit
Top-down processing – the operation in sensation and perception, launched by cognitive processing at the brains higher levels, that allows the organism to sense what is happening and to apply the framework to information from the world
Trichromatic theory – the theory stating that color perception is produced by three types of cone receptors in the retina that are particularly sensitive to different but overlapping ranges of wavelengths
Vestibular sense – sense that provides information about balance and movement
Volley principle – modification of frequency theory stating that a cluster of nerve cells can fire neural impulses in rapid succession producing a volley of impulses
Weber’s law – the principal that two minimum percentage (rather than a constant amount) to be perceived as different
How We Sense and Perceive the World
Sensation and Perception
Sensation and Perception are the ways by which we detect and understand various stimuli. Our world, in fact, is completely surrounded with stimuli. We don’t experience anything directly though, we instead receive a stimulus from the external environment and turn it into neural energy. It is then turned into an action potential that relays information about the stimulus through the nervous system to the brain. But it is not until the process of perception that you understood what you have sensed. For example, you may have touched something and sensed that you did indeed touch it, but once you recognize what that object was is perception.
Bottom-Up and Top-Down Processing
Bottom-up processing is just as described from the above paragraph, you sense something first and sensory receptors register information about the external environment and send it up to the brain for interpretation. Top-Down processing, on the other hand, begins with cognitive processing in the brain. It begins with at least some sense of what is happening and apply that to incoming information from the world. Both of these processes are applied together to allow us to function efficiently.
Why Do We Sense and Perceive
· To survive
o I.E. sensing a predator or seeing/smelling food.
Sensory Receptors and the Brain
· All sensation begins with sensory receptors
o Specialized cells that detect stimulus information and transmit it to sensory(afferent) nerves and the brain.
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· Sensory receptors are selective and have different neural pathways.
· Sense organs and sensory receptors fall into several main classes based on the type of energy that is detected including:
o Photoreception: detection of light
o Mechanoreception: detection of pressure, vibration, and movement
o Chemoreception: Detection of chemical stimuli, perceived as smell or taste.
· Sometimes, in very rare cases, the senses can become mixed or confused.
o Synaesthesia: an experience in which one sense induces an experience in another sense. For example, a person might be able to “taste” a color.
o Phantom Limb Pain: when an amputee still feels pain from a limb they have lost. Even though the sensory receptors are gone, the areas of the brain and nervous system that received information from those receptors are still there, thus causing the confusion.
Thresholds
· Absolute Threshold: the smallest amount of energy that a person can detect.
o When the energy of the stimulus falls below this threshold, we cannot detect its presence.
· Not everyone has the same level of threshold.
o Some people can smell, hear, or see better than others.
· Noise: irrelevant and/or competing stimuli.
o An extra stimulus that hinders your ability to detect the main stimulus.
· Difference Threshold: also known as “just noticeable difference” it is the degree of difference that must exist between two stimuli before the difference is detected.
o Weber’s Law: principle that states that two stimuli must differ by a constant proportion to be perceived as different.
Signal Detection Theory
· Signal Detection Theory: focuses on decision making about stimuli under conditions of uncertainty. This theory has two main components:
o Information Acquisition: what information is being communicated?
o Criterion: when you make a judgment based on what is communicated.
Perceiving Sensory Stimuli
· The Stroop Effect: refers to the way that automatically reading a color name can make it difficult to name the color in which the word is printed.
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· Novel Stimuli: stimuli that is new, different, or unusual.
· Emotion-induced blindness: refers to the fact that when encounter an emotionally charged stimulus, we often fail to recognize a stimulus that is presented immediately after it.
· Inattentional blindness: refers to the failure to detect unexpected events when our attention is engaged by a task.
Perceptual Set
· Perceptual Set: A predisposition or readiness to perceive something in a particular way. It reflects top-down influences on perception.

Sensory Adaptation
· Sensory Adaptation: A change in the responsiveness of the sensory system based on the average level of surrounding stimulation.
o Example: when you turn off the lights and you can’t see anything, but, after a little while, you can start to see in the dark.
Extrasensory Perception
· ESP: when a person can read another person’s mind or perceive future events in the absence of concrete sensory input.
o The scientific study of ESP is Parapsychology.
The Visual System


The Visual Stimulus and the Eye

Our ability to detect visual stimuli depends on the sensitivity of our eyes to differences in light.
Light

Light is a form of electromagnetic energy that can be described in terms of wavelengths. Light travels through space in waves. The wavelength of light is the distance from the peak of one wave to the peak of the next. Wavelengths of visible light range from about 400 to 700 nanometers. The wavelength of light that is reflected from a stimulus determines its hue, or color.
Waves of light can also be described in terms of their amplitude, or height. The amplitude determines the brightness of the stimulus. The saturation, or richness, of a visual stimulus is determined by the purity of the wavelengths, whether they are all the same or a mix of waves.
The Structure of the Eye
Your eye is composed of three parts – the sclera, iris, and pupil. The sclera is the white, outer part of the eye that helps to maintain the shape of the eye and to protect it from injury. The iris is the colored part of the eye. The pupil, which is the black dot in the middle, is the opening in the center of the iris. The iris has muscles that expand and contract, which determines how much light is let in.
The cornea and the lens bring the image into focus. The cornea is a clear membrane just in front of the eye, and the lens is a transparent, flexible disk-shaped structure filled with gelatin-like material. These parts of the eye bend the light that falls of the surface of your eye just enough so it focuses at the back. The older you get, the less flexibility your lens has, which makes it harder to go from a flattened shape to a rounded shape. This makes it less possible to bring objects into focus.
The multilayered retina, which is located at the back of the eye, is the light-sensitive surface that records electromagnetic energy and converts it to neural impulses for processing in the brain. The human retina has around 126 million receptor cells. They turn the electromagnetic energy of light into a form of energy that the nervous system can process. Rods and cones are the two kinds of visual receptor cells that differ in both how they respond to light and in their patterns of distribution on the surface of the retina. Rods are the receptors in the retina that are sensitive to light, but they are not very useful for color vision. Cones are the receptors that we use for color pigmentation.
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The most important part of the retina is the fovea, a tiny area in the center of the retina at which vision is at its best. Rods and cones at the back of the retina convert light into electrochemical impulses. The signal is transmitted to the bipolar cells and then moves on to another layer of specialized cells called ganglion cells. The axons of the ganglion cells make up the optic nerve, which carries the visual information to the brain for further processing.
The blind spot is the place on the retina where the optic nerve leaves the eye on its way to the brain. We can’t see anything that reaches only this part of the brain.
Visual Processing in the Brain
The optic nerve leaves the eye and carries information to the brain about light. In the brain, at a point called the optic chiasm, the optic nerve fibers divide, and about half of the nerve fibers cross over the midline of the brain. This means that what we see in the left side of our visual field is registered on the right side of our brain, and what we see in the right visual field is registered in the left side of the brain.
The Visual Cortex
The visual cortex, located in the occipital lobe at the back of the brain, is the part of the cerebral cortex involved in vision. Most visual information is processed in the primary visual cortex, and then moves to other visual areas for analysis. Feature detectors are neurons in the brain’s visual system that responds to particular features of a stimulus. The visual cortex has neurons that are individually sensitive to different types of lines and angles.
Parallel Processing
Parallel Processing, the simultaneous distribution of information across different neural pathways, quickly travels sensory information through the brain. To function in the world, we need to “see” all of these characteristics at once, which is parallel processing.
Binding
Binding is the bringing together and integration of what is processed by different pathways or cells. Binding involves the coupling of the activity of various cells and pathways. All the neurons throughout pathways that are activated by a visual object pulse together at the same frequency. This set of neurons appears to bind together all the features of the objects into a unified perception.
Color Vision
The two main theories of color are the trichromatic theory and the opponent-process theory. The trichromatic theory, proposed by Thomas Young in 1802 and extended by Hermann von Helmholtz in 1852, states that color perception is produces by three types of cone receptors in the retina that are particularly sensitive to different, but overlapping, ranges of wavelength. Young and Helmholtz reasoned that if the combination of any three wavelengths of different intensities is indistinguishable from any single pure wavelength, the visual system must base its perception of color on the relative responses of three receptor systems – red, blue, and green.
The study of defective color vision, or color blindness, provides further support for the trichromatic theory. The nature of color blindness depends on which of the three kinds of cones (red, blue, or green) is inoperative. In the most common form of color blindness, the green cone system malfunctions in some way.
Afterimages are sensations that remain after a stimulus is removed. Color afterimages involve particular pairs of colors.
The opponent-process theory, Ewald Hering’s view, states that cells in the visual system respond to red-green and blue-yellow colors; a given cell might be excited by yellow and inhibited by blue, whereas another cell could be excited by red and inhibited by green. Hering’s theory explains afterimages.
Both the trichromatic theory and the opponent-process theory are accurate because the red, blue, and green cones in the retina are connected to retinal ganglion in such a way that the three-color code is immediately translated into the opponent-process code.
Perceiving Shape, Depth, Motion, and Constancy
Perceiving visual stimuli means organizing and interpreting the fragments of information that the eye send to the visual cortex. Among these dimensions of what we see are shape, depth, motion, and constancy.
Shape
We see shapes because they are marked off from the rest of what we see by contour, a location at which a sudden change of brightness occurs. The figure-ground relationship is the principle by which we organize the perceptual field into stimuli that stand out and those that are left over. The figure-ground relationship is a gestalt principle. Gestalt in German for “configuration” or “form”, and gestalt psychology is a school of thought interested in how people naturally organize their perceptions according to certain patterns. One of gestalt psychology’s main principles is that the whole is different from the sum of its parts.
Depth Perception
Depth perception is the ability to perceive objects three-dimensionally. To perceive a world of depth, we use two kinds of information, or cues – binocular and monocular. Binocular cues are depth cues that depend on the combination of the images in the left and right eyes and on the way the two eyes work together. The pictures are slightly different because the eyes are in slightly different positions. The disparity, or difference, between the images in the two eyes is the binocular cue the brain uses to determine the depth, or distance, of an object.
Convergence is another binocular cue to depth and distance. When we look at something, our eyes converge, or move together, almost crossing. Monocular cues, or depth cues, are powerful depth cues available from the image in one eye, either the right or the left. Examples of monocular cues are familiar size, height in the field of view, linear perspective and relative size, overlap, shading, and texture gradient.
Motion Perception
In humans, the brain takes over the job of analyzing motion through highly specialized pathways. Humans have neurons that are specialized to detect motion, and feedback from our body tells us whether we are moving or whether someone or some object is moving. Apparent movement occurs when we perceive a stationary object as moving.
Perceptual Constancy
Retinal images change constantly. Perceptual constancy is the recognition that objects are constant and unchanging even though sensory input about them is changing. We experience three types of perceptual constancy – size constancy, shape constancy, and color constancy.
We interpret sensation. We perceive objects as having particular characteristics regardless of the retinal image detected by our eyes. Images may flow across the retina, but experiences are made sensible through perception.
The Auditory System: How We Experience It
Sound waves are vibrations in the air that are processed by the auditory system. Wavelength determines the sound waves frequency, that is , the number of full wavelengths that pass an interval point. Pitch is perceptual interpretation of the frequency of the sound. High and low pitch differentiation. Amplitude is the volume measures in decibels (dB), the force of the air pushing your ears, higher the amplitude more force, lower less force.
Structure: Outer, Middle and Inner Ear
Outer ear consists of the pinna and the external auditory canal. Pinna collects the sound and channels into the interior of the ear. Cats of other animals have the ability to move there pinna in the direction of a sound to hear it better, humans do not have the ability.
Middle ear is made up of the eardrum, hammer, anvil and stirrup. Eardrum or tympanic membrane separates the outer ear from the middle ear and vibrates in the responds to noise or sound Hammer, anvil and stirrup are three of the smallest bones in the body and they are connected in the ear. When these three bones vibrate the information in carried to the fluid in the inner ear. Muscles in the middle ear can maneuver the chain of bones to amplify sounds and also work to decrease the intensity of sound and protect the inner ear.
Inner Ear includes the oval window, cochlea and the basilar membrane. The purpose of the inner ear is to convert sound waves into neural impulses and send them to the brain. The oval window transmits sounds to the cochlea. The cochlea is a tubular, fluid filled structure that is coil like a snail. The basilar membrane lines the inner wall of the cochlea and run the entire length. The flexibility of the basilar membrane allows vibrations to be more intense when exposed to different sound frequencies. Hair cells line the basilar membrane, and these hairs are like little receptors such fine hair are cilia, the movement of hair cells against the tectorial membrane which transmits to the brain.
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Theories of Hearing
Place theory states each frequency produces vibrations at a specific part of the basilar membrane. Place theory explain high frequency but not low frequency, low frequencies haven’t been identified in a specific area of the basilar membrane.
Frequency theory explains lower frequency hearing. Starting at the perception of the sounds frequency depends on how often the auditory nerve fires. Firing happens more often in high frequency than in lower frequencies. One neuron can only fire a thousand times a second, one limitation of the frequency theory.
The Volley Principle was created to address the limitations of the frequency theory. Volley principle states that a group of neurons work together to share firing.
Auditory Processing in the Brain
Past the inner ear is the auditory nerve which carries the sound to the brain. It is more difficult to convert sound to chemical in the brain than visual. The auditory nerve is responsible for transporting sound information to the brain. Through electrochemical transport many synapse occur in the ascending auditory pathway, with most fiber cross the midline of the hemispheres on the cerebral cortex, although some go the receptive side left ear to right hemisphere and right ear to left hemisphere. The auditory nerve connects from the cochlea to the brain stem.
Localizing Sound
Having two ears like having two eyes helps us locate where a sound is coming from. Shadow noise is your ears ability to tell whether a sound is more intense on the left or the right. Time and intensity of the sound help locate sound as well.
Other Senses
Skin Senses are touch, temperature and pain these are the cutaneous senses. Touch is pressure against the skin and the ability to feel. Temperature has thermoreceptors are nerve endings under the skin that heat and cool the body as needed. Pain warns the body of danger. Pain receptors have a higher threshold for firing.
Chemical Senses: Smell and Taste
Tastes receptors are bumps on the tongue called papillea which contain taste buds. About 10,000 taste buds on your tongue. Taste buds are replaced every two weeks. Older people have about 5,000 up and working. Taste is traditionally characterized as sweet, sour, bitter and salty-these underestimate the complexity of taste. New taste are being discovered, the taste Umani which is Japanese for delicious. Just to say our tastes go for beyond sweet, sour, bitter and salty.
Smell is used to distinguish between rotten and fresh food and which foods made us sick in the past. Although can’t smell to the capacity of other animals we can use smell to track gas or smoke. The nose is an active instrument sniffing is how we find things. Olfactory Epithelium line the roof of the nasal cavity that contains sheets of receptor cells for smell. From there it travels to the temporal lobe and can bring up emotion and memory.
Kinesthetic and Vestibular Senses
Kinesthetic provide information about movement, posture and orientation. This has no specific organ instead it’s imbedded in muscle fibers and joints. The sense you don’t notice till it’s gone, like walking with your leg asleep all the time.
Vestibular sense tells us if our head is tilted, moving, slowing down or speeding up. Semicircular canals of the inner ear contain the sensory receptors that detect head motion caused when we tilt or more our and /or body. The canals consist of right-left, up-down, and front-back planes and are fluid-filled. Pathway to the vestibular sense start in the auditory nerve which both the cochlear nerve(with sound information) and the vestibular nerve (with information about balance and movement).
Both the kinesthetic and vestibular systems work together to coordinate the body. This is also known as proprioceptive feedback, which is information about the position of our limbs and body parts in relation with our other body parts. This is something that would be important for playing any sport.
Video: http://www.youtube.com/watch?v=7w5YkPsPlSc
Questions
Q: What are sensory receptors?
A: Specialized cells that detect stimulus information and transmit it to sensory nerves and the brain
Q: What is Weber’s law?
A: Two stimuli must differ by a constant proportion to be perceived as different.
Q: The eye is composed of what three parts?
A: The sclera, Iris, and Pupil
Q: What allows us to see three dimensionally?
A: Depth perception
Q: What are the names of the three bones in the middle ear?
A: Hammer, Anvil and Stirrup