Chapter 4 Sensation and Perception

Threshold example:

Hardware stores sell a gadget with a photocell that automatically turns a lamp on when a room gets dark. The level of light intensity at which the gadget clicks on is its threshold.

Amplitude

Height. Affects mainly the perception of brightness

Shadows:

Help us gauge sizes as well as location of objects

Optic disk

Hole in the retina where the optic nerve fibers exit the eye. Known as the blind spot.

Purity

How varies the mix is. Influences the perception of the saturation, or richness, of colors.

Two types of receptors in retina

Rods and Cones

False Alarms

Detecting signals when they are not present

Hits

Detecting signals when they are present

Gestalt psychology:

A field that focuses on our ability to perceive overall patterns. We perceive complex patterns as a whole! Rejects the idea that a perception can be broken down into components.

Just noticeable difference

A just noticeable difference (JND) is the smallest difference in stimulus intensity that a specific sense can detect. An absolute threshold is simply the just noticeable difference from nothing (no stimulus input) to something. In general, as stimuli increase in magnitude, the JND between them becomes larger. However, the size of a just noticeable difference in a specific sense tends to be a constant proportion of the size of the initial stimulus.

Cones:

Adapted for color vision, daytime vision, and detailed vision; three cones

Rods

Adapted for vision in dim light; one rod

Absolute threshold

An absolute threshold for a specific type of sensory input is the minimum stimulus intensity that an organism can detect. researchers arbitrarily defined the absolute threshold as the stimulus intensity detected 50% of the time.

Linear perspective:

As parallel lines stretch farther our over the horizon, they come closer together

Common Visual Deficiencies:

Attributed to the light not being focused clearly on the retina.

Subliminal

Below threshold

Eye serves two main purposes:

Channel light to the neural tissue that receives it, called the retina, and they house that tissue.

Nearsightedness

Close objects are seen clearly but distant objects appear blurry because of the focus of light from distant objects falls a little short of the retina. Problem occurs when the cornea or lens bends light too much, or when the eyeball is too long.

Iris

Colored ring of muscle surrounding the pupil

Dilated pupils vs constricted

Constricted lets less light into the eye, but they sharpen the image falling on the retina. dilated pupils (opens more), they let more light in, but the image is less sharp.

Gustav Fechner

Contributed to psychophysics and published pioneering work on the subject in 1860. German scientist that worked at the University of Leipzig, where Wilhelm Wundt later founded the first formal laboratory. Laid foundation that Wundt built upon.

Wavelength

Distance between peaks. Affects mainly the perception of color.

Farsightedness

Distance objects are seen clearly but close objects appear blurry because the focus of light from close objects falls behind the retina. Problem typically occurs when the eyeball is too short.

Threshold

Dividing point between energy levels that do and do not have a detectable effect.

Misses

Failing toe detect signals when they are present

Texture gradients:

Farther the way, the more "packed together" the appearance is

Vision

Filter that permits people to sense but a fraction of the real world.

Visual Agnosia

Inability to recognize objects through sight

How to see:

Incoming visual input must be converted into neural impulses that are sent to the brain.

Retina:

Layer of visual receptors covering the back surface of the eyeball. Location of the rods and cones.

Crystalline Lens

Lens, located behind the cornea. Forms an upside down image of objects on the retina.

Absolute Threshold

Minimum stimulus intensity that an organism can detect. Defines the boundaries of an organism's sensory capabilities. As stimulus intensity increases, subjects' probability of responding to stimuli gradually increases.

Rods

More elongated. Outnumber cones by a huge margin, as humans have 100-125 million rods.

Cones

More stubbier and there are only 5-6.4 million cones. Specialized visual receptors that play a key role in daylight vision and color vision. handles most of people's daytime vision because bright light dazzles the rods. Do not respond well to dim light. Provide better visual acuity, sharpness and precise detail. Concentrated more heavily in the center of the retina.

Retina

Neural tissue lining the inside back surface of the eye; absorbs light, processes images and sends visual information to the brain. Contains millions of receptor cells that are sensitive to light.

Correct Rejections

Not detecting signals when they are absent

Accomodation

Occurs when the curvature of the lens adjusts to alter visual focus. When you focus on a close object, the lens of your eye gets fatter (rounder) to give you a clear image. When you focus on distant objects, the lens flattens out to give you a better image.

Signal detection theory

Proposes that the detection of stimuli involves decision processes as well as sensory processes, both of which are influenced by a variety of factors besides stimulus intensity, such as noise and your expectations. In comparison to classical models of psychophysics, signal detection theory is better equipped to explain some of the complexities of perceived experience in the world.

Saturation

Refers to the less whiteness seen in a color, the more saturated it is.

Subliminal Perception

Registration of sensory input without conscious awareness is another term for threshold. Related to controversies like money, sex, religion and rock music.

Pupil

Regulates the amount of light entering the eye because it controls the size of the pupil. Opening in the center of the iris that permits light to pass into the rear chamber of the eye.

Perception

Selection, organization, and interpretation of sensory input.

Stimulus

Sensation begins with stimulus, any detectable input from environment.

Definition of sensation vs. perception:

Sensation involves the stimulation of sensory organs, whereas perception involves the interpretation of sensory input. The two processes merge at the point where sensory receptors convert physical energy into neural impulses.

Sensory adaptation

Sensory adaptation is a gradual decline in sensitivity to prolonged stimulation. E.g. getting used to the smell of garbage

Just Noticeable Difference (JND):

Smallest difference in stimulus intensity that a specific sense can detect. Close cousins of absolute thresholds. As stimuli increase in magnitude, the JND between them becomes larger.

Psychophysics

Study of how physical stimuli are translated into psychological experience

Visual cues that suggest depth

Texture gradients, Shadows, Detail

Sensation

The stimulation of sense organs. Sensation involves the absorption of energy, such as light or sound waves, by sensory organs, such as the eyes and ears.

Feature detectors represent bottom up process:

Tiny elements combine larger items. Feature detection is not enough. Perception also includes top-down process, in which you apply your experiences and expectations to interpret what each item must be in context (see page 128 for picture examples)

Fovea

Tiny spot in the center of the retina that contains only cones; visoual acuity is greatest at this spot.

Cornea

Transparent "window" at the front.

Lens

Transparent eye structure that focuses the light rays falling on the retina. Made up of relatively soft tissue, capable of adjustments that facilitate a process called accommodation.

Physical quality of light that corresponds to color (wavelength)

Wavelength affects our perception of color

Detail:

We see objects that are closer in more detail

Light

a form of electromagnetic radiation that travels as a wave, moving, naturally enough at the speed of light.

Opponent process theory of color vision

a. we perceive color in terms of paired opposites: red vs. green, yellow vs. blue, and white vs. black b. example of the negative afterimages

Function of rods

detects dim light, more responsive to faint stimulation that a cone is

Function of the lens

the function of the lens is to enable focus of an object - the lens is a flexible structure that can vary in thickness, enabling the eye to accommodate. It bends entering light rays and focuses them on onto the retina.