PSY 100: CH 4 McGraw Hill

sensation

the process by which our sensory receptors and nervous system receive information from the environment through stimuli (physical response)

perception

the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events (psychological response)

stimulus

any event or source of energy that evokes a response a sense organ

absolute threshold

the minimum stimulation (intensity) needed to detect a particular stimulus 50% of the time

noise

anything that interferes with, distorts, or slows down the transmission of information or other senses

difference threshold

The smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred.

Weber's law

the just noticeable difference of a stimulus is a constant proportion despite variations in intensity; holds for every type of sensory stimuli (vision, sound, taste, etc.)

For example, Weber found that the just noticeable difference for weight is 1:50. the just noticeable difference distinguishing changes in loudness between sounds is larger for sounds that are initially loud than it is for sounds that are initially soft -- but proportional increase remains the same

- why we're startled by a phone ringing in a quiet room than when we're in a large crowd of people and it's noisy

sensory adaptation

tendency of sensory receptor cells to become less responsive to a stimulus that is unchanging due to constant stimulation/exposure

why is there a decline in sensory stimulation over time?

sensory nerve receptors cannot sustain a reaction and continue firing off messages to the brain for an indefinite period of time -- we pay the most attention to changes in our environment as a result

visual spectrum

the range of wavelengths that our eyes can detect

eyes and neurons

neurons make up a small percentage of the total eye, since the eye is like a mechanical device similar to a nonelectrical camera. however, the processing of visual images is more like a computer.

- our eyes convert light to a form that can be sent to the brain as messages

how does light enter the eye?

1. ray of light reflected off an object first travels through *cornea*, which has a curvature that bends (refracts) the light in a way that allows it to focus light more sharply.

2. then, the light moves through the *pupil*, with the size of the pupil opening depending on the amount of light in the surrounding environment (dimmer surroundings = pupil opens more to allow more light to enter)

3. light moves through *lens*, the transparent structure behind the pupil that changes shape to help focus images on the retina

structure of eye

cornea, pupil, iris, lens, retina

lens accommodation

the process by which the eye's lens changes in thickness to focus near or far objects on the retina

- flat when viewing objects far away

- round when viewing objects up close

retina

Contains sensory receptors that process visual information and sends it to the brain

although images that travel through the lens are reversed, the brain...

automatically interprets the image in its original position

rods

Retinal receptors that detect black, white, and gray; play key role in night vision and peripheral vision (seeing objects outside main center of focus); highly sensitive to light

cones

retinal receptor cells that are concentrated near the center of the retina, on the *fovea*, and that function in daylight or in well-lit conditions. The cones detect fine detail and give rise to *color* sensations.

dark adaptation

the recovery of the eye's sensitivity to visual stimuli in darkness after exposure to bright lights; time in dark before rods regain maximum light sensitivity

- cones reach max level of adaptation in few minutes, but it takes 20-30 minutes for rods

light adaptation

the recovery of the eye's sensitivity to visual stimuli in light after exposure to darkness; occurs much faster than dark adaptation (few minutes)

sending the message from the eye to the brain

what happens to light when it reaches the retina depends on if it hits a rod or cone

- rods have rhodopsin, a complex reddish-purple protein whose composition changes chemically when energized by light

- cones have different substances but similar principles

- stimulation of rods and cones triggers neural response that is sent to other nerve cells in retina called *ganglion* and *bipolar* cells

bipolar cell

a bipolar neuron located in the middle layer of the retina, conveying information from the rods and cones and transmits them to the ganglion cells

ganglion cell

a neuron located in the retina that receives visual information from bipolar cells; its axons bundle up to give rise to the optic nerve, in which visual info is sent out the back of the eyeball to the brain through the optic nerve

optic nerve

bundle of ganglion axons that carries neural impulses from the eye to the brain

optic chiasm

the point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain

processing the visual information

- ultimately takes place in visual cortex of brain

- visual info coming from individual neurons are combined and processed by different parts of the brain in a jointly manner (for example, one part of brain processes shapes, another part processes colors, etc.)

- highly specialized, as there are also parts of brain that are involved in the perception of certain kinds of stimuli (ex. reacting to human faces, nonhuman animal faces, and inanimate stimuli)

- process occurs in several levels simultaneously

feature detectors

neurons that respond selectively to very specific features of more complex stimuli, such as shape and pattern

trichromatic theory of color vision

The theory that there are three kinds of cones in the retina -- *blue-violet, green, and yellow-red*. each of which responds primarily to a specific range of wavelengths; perception of color is influenced by the relative strength with which each of the three kinds of cones is activated (ex. if we see a blue sky, the blue-violet cones are mostly activated while the others show less activity

- validity of this theory is questioned by *afterimage*

afterimage

a visual experience that occurs after the original source of stimulation is no longer present (activity in retina continues)

Opponent-process theory

The theory that color vision is the product of opposing pairs of color receptors, red-green, blue-yellow, and black-white; when one member of a color pair is stimulated, the other member is inhibited.

- operates later stages of neural processing in brain

- can explain afterimage effect

blind spot

the point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there

Reflex sympathetic dystrophy syndrome

constant intense pain that is out of proportion to an injury

skin senses

the sensations of touch, pressure, temperature, and pain

- helps us become aware of potential dangers to our bodies

which area of the body has many more receptor cells sensitive to touch compared to most areas on the body?

fingertips

explanation for pain

cell injury -- damaged cell releases chemical called substance P that transmits pain messages to the brain

pain is a perceptual response that...

depends heavily on our emotions and thoughts, and may also be linked to certain genes (women experience pain more intensely than men)

how to reduce/shut off painful stimuli

- other impulses from a different stimuli can overwhelm the nerves related to pain, in which the non painful stimuli can outcompete the neural message of pain.

- can be shut off by psychological factors related to a person's current emotions, interpretation of events, and previous experiences (some soldiers who are injured may not feel pain due to feeling relief from being alive)

- natural ways such as release of endorphins

Synethesia

stimulation of one sensory system involuntary leads to a person to experience an additional sensory response in a different sensory system

- people with synesthesia may have unusually dense neural linkages between between the sensory areas of the brain; another hypothesis says that they lack neural controls usually inhibit connections between different sensory systems

multimodal perception

the approach that considers how information that is collected by various individual sensory systems is integrated and coordinated

Gestalt Psychology

A series of principles that describe how we perceive and interpret sensory information at the whole level rather than in terms of their component features (bits and pieces)

- whole is greater than the combination of its individual parts

Gestalt principles

closure, proximity, similarity, simplicity

closure

the tendency to complete figures that are incomplete

proximity

elements closer together are grouped together

similarity

the tendency to perceive things that look similar to each other as being part of the same group

simplicity

viewers tend to organize elements in the simplest way possible

top-down processing

information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations

- allows us to fill in the gaps in ambiguous and out-of-context situations

bottom-up processing

the analysis of the smaller features to build up to a complete perception

- looking at individual components of the stimuli first

only when we can consider both what our senses detect (_______) and the context or meaning our brain interprets (________), can we fully understand how we perceive our world.

bottom-up processing

top-down processing

depth perception

the ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance

- largely due to fact that we have two eyes

- certain difference between the two eyes causes two different images to reach retina; the brain integrates the two images into one view while also recognizing the difference. it uses the difference between the images to estimate the distance of the object from us

binocular disparity

the difference in images between the two eyes, which is greater for objects that are close and smaller for distant objects

monocular cues

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

motion parallax (monocular cue)

a depth cue in which the relative movement of elements in a scene gives depth information when the observer moves relative to the scene

- for example, you are a passenger in a car. when focusing on one object outside, the objects in front of it seem to be moving backwards, and the nearer the object is to you the faster it seems to move; while the objects behind it seem to be moving in the same direction as you but at a slower speed.

relative size

a monocular cue for perceiving depth; the smaller retinal image, although may be the same size as another object, appears farther away

texture gradient

a monocular cue for perceiving depth; a gradual change from a coarse distinct texture to a fine, indistinct texture signals increasing distance. objects far away appear smaller and more densely packed

Parallel processing

The brain's ability to handle multiple streams of sensory or cognitive information at the same time

perceptual constancy

perceiving objects as unchanging (having consistent lightness, color, shape, and size) even as illumination and retinal images change

- experience teaches us that the size of an object stays constant

- may explain moon illusion

apparent movement

the perception that a stationary object is moving -- occurs when different areas of the retina are quickly stimulated

subliminal perception

the processing of information by sensory systems without conscious awareness (stimuli is presented so quickly it isn’t detected)

Priming

Words or pictures that are not consciously perceived but may nevertheless influence people's judgments, attitudes, and behaviors

Binding

Your brain combines information from different senses into one experience.

Binocular convergence

Your eyes turn inward toward each other when looking at something close.

Figure-Ground Relationship

Your brain separates what you're focusing on (figure) from the background (ground).

Kinesthetic senses

Your sense of where your body parts are and how they are moving, even without looking at them.

Perceptual set

Your expectations and past experiences influence what you see or hear.

Vestibular senses

Your sense of balance and body position, mainly controlled by structures in your inner ear.

Signal Detection Theory

How we decide whether something we notice is a real signal or just background noise.

Subliminal Perception

Your brain notices or processes something without you consciously realizing it.

Stroop effect

It is harder to name the color of a word when the word itself says a different color.

Types of sensation

Photoreception: vision, light

Mechanoreception: touch, pressure, movement

Chemoreception: smell, taste (chemicals)

Deafferentation

Brain makes up missing information, resulting in hallucinations