Psychology – Mr. Duez                         LEARNING TARGETS                               UNIT 2-  "Sensation & Perception"

If you learn only 4 things...

1. Perception is the interpretation of sensory information; it relies on experience.

2. The difference between sensation and perception

3. The structure and function of the eye

4. The structure and function of the ear

Sensation and perception are areas that have been of interest to psychologists for most of the history of psychology. As we sit here, our senses receive literally thousands of messages. We need to make sense of this information. Our senses take in the information, and they do so from birth. Yet the interpretive part -perception- requires knowledge.

In this chapter, we will discuss the first two senses and then how those senses pass the raw data on to the perceptual processes we have developed over time.

English physicist Sir Isaac Newton, in an experiment, observed that a ray of sunlight, or white light, was broken up into the brilliant colors of the spectrum when it passed through a glass prism. He then noticed that the ray recombined into white light when it was beamed back through another prism. It occurred to Newton that since light rays are not colored, color must not be an actual physical quality in the world. He concluded that color must exist only in the mind and not in nature.

If color does not actually exist in the world around us, then where do colors come from? To answer this question, we will need to understand how our visual sensory system translates different wavelengths of light into neural impulses so that our brain can interpret the information it receives as the sensation of color.

The other types of sensation we experience - such as sound, smell, taste, touch, and pain - are also products of the brain’s response to various kinds of sensory stimuli. But, typically two main types of systems are described when discussing sensation: vision & hearing. They are the most powerful ways that humans experience their world.

1.  Psychophysics: Basic Concepts and Issues in Measuring Perception

One key to understanding perception is the accurate measurement of the processes of perception. Psychologists have worked hard to develop strategies for measuring perception. The concepts are not nearly as clear as other concepts in psychology, but let’s address some of these measurement techniques.

Psychophysicists use a variety of methods to relate sensory inputs to subjective perception. Thresholds are limits of your perception. The absolute threshold is the least amount of information for our ability to perceive a stimulus. A difference threshold is similar to absolute in that it is the amount of stimulus needed to determine a change in a stimulus.

Absolute thresholds are not really absolute.

Weber's law states that the size of a JND is a constant proportion of the size of the initial stimulus.

Fechner's law states that larger and larger increases in stimulus intensity are required to produce JND in the magnitude of sensation.

Signal-detection theory = the detection of sensory inputs is influenced by noise in the system & by decision-making strategies. It replaces Fechner's sharp threshold w/ detectability & emphasizes that factors besides stimulus intensity influence detectability.

Signal-Detection Theory addresses how participants are able to perceive information from the world. It argues that there is either a detected stimulus (a hit), a miss, a correct rejection, or a false positive. A participant is presented with a variety of stimuli, and each judgement is recorded. Good ability to detect results in more hits than misses and more correct rejections than false positives.

2.  Our Sense of Sight: The Visual System

Light varies in terms of wavelength, amplitude, & purity.

Light enters the eye through the cornea (part of the eye responsible for bending light) & pupil & is focused upside down on the retina by the lens.

The pupil is very important for vision. The pupil changes size depending on the amount of ambient light present. If there is a lot of ambient light, the pupil constricts to limit the amount of light coming in. If there is a lot of surrounding darkness, the pupil dilates to allow in as much ambient light as possible.

The lens is just behind the pupil. The lens works in conjunction with the cornea to bend light so that it falls on the appropriate space in the rear of the eye.

White part of the eye = sclera. It is filled with blood vessels to provide nutrients to the eye. In addition, the sclera provides structure to the eye.

Nearsighted = Distant objects appear blurry.

Farsighted = Close objects appear blurry.

Retina = neural tissues in eye, absorb light, process images, & send visual signals to the brain. It is the structure most responsible for visual acuity. The retina stretches across the back half of the eye, with a differential distribution of types of cells across the structure.

Retina - transforms light into neural impulses & send info to brain through optic nerve. Receptive fields are areas in retina that affect the firing of visual cells. Optic nerves from the inside 1/2 of each eye cross at the optic chiasm & then project to the opposite side of the brain.

Rods & Cones are two types of photoreceptor cells that directly receive light stimulation.

Cones (in fovea or center of the retina) key role in daylight vision and color perception.

Rods (greatest density just outside of fovea) - critical to night & peripheral vision. Dark/Light adaptation involve changes in the retina's sensitivity to light - allowing the eye to adapt to changes in illumination.

Bipolar cells in the first layer translate the information from rods and cones back out to the ganglion cells. Ganglion cells then transfer the information down toward the optic nerve. The point where the optic nerve exits the eye is a blind spot. You cannot see anything because there are no photoreceptors at the point at which those cells exit the retina.

The information is carried down the optic nerve, where it undergoes additional processing. Color information is added at the thalamus. At the end of the optic nerve is the occipital lobe, the structure most responsible for visual processing.

Perceptions of color (hue) are primarily a function of light wavelength, while amplitude affects brightness & purity affects saturation. 2 types of color-mixing: additive & subtractive. Human color perception depends on processes that resemble additive.

Trichromatic theory = people have 3 types of receptors sensitive to red, green & blue.

The opponent process theory = color perception depends on receptors that make antagonistic responses to red vs green, blue vs yellow, & black vs white. The evidence now suggests that both theories are necessary.

Reversible figures & perceptual sets demonstrate that the same visual input can result in very different perceptions. According to feature analysis theories, people detect specific elements in stimuli & build them into recognizable forms through bottom-up processing. However, form perception also involves top-down processing, which progresses from the whole to the elements.

Gestalt psychology emphasized that the whole may be greater than the sum of its parts (features), as illustrated by Gestalt principles of form perception (figure-ground, proximity, similarity, closure, & simplicity).

Binocular cues such as retinal disparity & convergence can contribute to depth perception (depends primarily on monocular cues - texture gradient, linear perspective, light & shadow, interposition, relative size, & height in plane).

Conscious perceptions of geographical slant (visual & verbal estimates of pitch), tend to be greatly exaggerated. Haptic (tactile) judgments seem largely immune to this perceptual bias. Perceptual constancies in vision help viewers deal with ever-shifting nature of proximal stimuli. A proximal stimuli is one that is received and transformed by the perceiver, while the distal stimulus is the stimulus in the environment. We do not  have direct access to information in the world. Rather, we use what our senses gather to make sense of the world. We use the information gathered from the distal stimulus to generate the proximal stimulus so that we have a representation of the world.

Optical illusions demonstrate that perceptual hypotheses can be inaccurate & perceptions are not simple reflections of objective reality (research: Muller-Lyer & Ponzo illusions).

3.  Our Sense of Hearing: The Auditory System

Like the visual system, the auditory system is a mechanical system designed to translate external stimuli into a code that is understandable by the brain. The mechanical process of audition is very interesting, and in many ways, it is amazing that it works as well as it does. The main goal of the auditory system is to translate acoustic energy into sound. It does this by passing sound waves down through the ear until specialized cells are able to translate this sound into code that is interpretable.

1st structure of the ear: pinna, or external ear. Pinna is the part of the ear that we see. Composed of cartilage & fat deposits, serves to funnel sound into the ear. The pinna is not essential - if you don’t have one, you can still hear - yet the pinna helps us determine the location of sound in space by providing us with a more efficient collection of sound.

Inside pinna: auditory canal. 2.5 centimeters in length, the longest depression in the skull. Purpose is to focus sound waves toward the tympanic membrane or eardrum: a thin tissue stretched over a bone, vibrates in sympathy with the sound waves, creating a message of the same amplitude as the original sound waves.

Sound waves are physical features. Sound varies in terms of wavelength (frequency), amplitude, & purity. Mainly they are perceptions of pitch, loudness, & timbre. Human ear sensitive = 2000 & 4000 Hz. Brief exposure to 120+ decibels can be painful & damaging.

Sound transmitted through external ear via air conduction to the middle ear, sound waves are then translated into vibration of tiny bones called ossicles (the malleus - or hammer, the incus - or anvil, and the stapes - or stirrup). These are the smallest bones in the human body and they work together to move the sound from the tympanic membrane into the inner ear. The bones vibrate in sympathy with the sound waves that are causing the tympanic membrane to vibrate. The bones end at the beginning of the inner ear.

The inner ear is the location of the cochlea. The cochlea is fluid filled. Here fluid conduction vibrates hair cells along the basilar membrane in the cochlea (hair cells are the receptors for hearing).

Place theory = pitch perception depends on where vibrations occur along the basilar membrane. 

Frequency theory = pitch perception depends on the rate at which the basilar membrane vibrates.

Modern evidence = the theories are complementary rather than incompatible.

Auditory localization involves locating the source of a sound in space. People pinpoint where sounds have come from by comparing inner ear differences in the intensity & timing of sounds.

4. Our Chemical Sense: Taste and Smell

Taste buds are sensitive to 4 basic tastes: sweet, sour, bitter, and salty. Distributed unevenly across the tongue.

Taste preferences = learned & heavily influenced by cultural background. Flavor influenced by odor of food.

Smell is a chemical sense. Chemical stimuli activate receptors lining the nasal passages = olfactory cilia. Most receptors respond to multiple odors.

5.  Our Sense of Touch: Sensory Systems in the Skin AND Our Other Senses (Kinesthetic & Vestibular)

Sensory receptors in the skin respond to pressure, temperature, & pain. Tactile localization depends on receptive fields similar to those seen for vision. Some cells in the somatosensory cortex appear to function like feature detectors. There are nerve fibers that respond specifically to warmth and cold.

Pain signals are sent to the brain along two pathways that are characterized as fast & slow. The perception of pain is highly subjective & may be influenced by mood, attention, and culture.

Gate-control theory holds that incoming pain signals can be blocked in the spinal cord. Endorphins and a descending neural pathway appear responsible for the suppression of pain in the central nervous system. Kinesthetic system monitors the position of various body parts. Receptors in joints/muscles send signals to the brain along the same pathways as tactile stimulation.

Sense of balance is primarily dependent on activity in the semicircular canals in the vestibular system.


1. When physical energy is transformed into neural impulses, it is referred to as

(reception, transduction, perception, sensation, induction)

2. An object as it appears in the world as a visual stimulus is referred to as

(distal stimulus, proximal stimulus, figure, ground, retinal image)

3. ____ is receiving data from the external environment; ____ is how our brains make sense of that data.

(induction; reception … gestalt; detection … comprehension; transduction … perception; sensation … sensation; perception)

4. The amount of stimulus required to determine that a stimulus has changed just a little bit is called the

(difference threshold, absolute threshold, just noticeable difference, just noticeable threshold, taste aversion)

5. The part of the eye responsible for receiving photons of light and then translating them into neural messages is the

(sclera, lens, cornea, pupil, retina)

6. The part of the ear responsible for translating information into neural impulses is the

(pinna, cochlea, semicircular canals, tympanic membrane, incus)

7. The part of the retina in which there is no visual receptors is the point at which the optic nerve exits the eye. What is the term for this point?

(rod, blind spot, cone, fovea, pupil)

8. What is the term for the smallest amount of a sensation that is necessary for a person to actually notice that it is present?

(absolute threshold, difference threshold, perceptual set, perceptual adaptation, sensory adaption)

9. The part of the brain responsible for coding auditory information is the

(temporal lobe, occipital lobe, somatosensory cortex, frontal lobe, hypothalamus)

10. The part of the brain responsible for coding visual information is the

(temporal lobe, somatosensory cortex, hypothalamus, occipital lobe, frontal lobe)

11. The __ is the first structure involved in focusing photons of light.

(cornea, lens, retina, sclera, vitreous humor)

12. In signal detection theory, when a participant responds that a stimulus was present and it was, the response is called a

(correct rejection, ROC curve, miss, hit, false positive)

13. Gestalt principles are used to make order out of perceptions so that we see things as connected and not just random bits of information. Which of these is NOT a common Gestalt principle?

(Similarity, Localization, Closure, Proximity, Good continuation)

14. The structure in the eye that changes shape to accommodate the closeness or distance of an object is the

(cornea, retina, lens, sclera, iris)

15. The structure in the ear that is responsible for gathering sound initially is the

(pinna, tympanic membrane, cochlea, semicircular canals, stapes)

16. The receptor cells that make the transduction for the auditory system are called the

(basilar membrane, hair cells, cochlea, semicircular canals, stapes)

17. The cells responsible for coding for color in the eyes are the

(rods, iris, cones, retina, fovea)

18. The point of the focus for the eye that contains mostly cones is the

(rods, iris, cones, retina, fovea)

19. Which part of our auditory system is best able to aid us in the localization of sounds?

(Ossicles, Pinna, Tympanic membrane, Occipital lobe, Eardrum)

20. The structure that contains the main receptor cells in the auditory system is the

(semicircular canals, tympanic membrane, pinna, malleus, cochlea)