Preview p.24• What do you see? Describe the sensory processing that is

occurring as you view this painting.

The Forest Has Eyes

Sensation

pp.196-208NB p.25

Objective 1: What is the difference between bottom-up and top-down processing?

• Bottom-up processing: analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information

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

Objective 1: What is the difference between sensation and perception?

• Sensation: the detection of physical stimulus in the environment.

• Perception: the interpretation of sensation.

Psychophysics

• The study of relationships between physical stimuli, and our psychological experience of them.

• Gustav Fechner

Objective 2: What is the difference between absolute and difference thresholds?

• Absolute threshold: the smallest amount of stimulus energy necessary for sensation to take place 50 percent of the time.

• Difference threshold: the just noticeable difference (JND); the smallest detectable “difference” between two stimuli

Subliminal Messages

• Brief auditory or visual messages presented below the absolute threshold so there is less than a 50% chance they will be detected– Used in advertisements, motivation

• Little effect according to psychological research.

• Subliminal Messages are illegal in the United States to use in TV and radio

Can you see the arrow?

Hidden Messages

• They are not subliminal! They are above the absolute threshold, but just barely. You have to seek them out.

Hidden Mickey

Why Hidden Messages?• They include sexual messages to get the interest

of adults, so that the cartoons are not just of interest to children.

• They make the movie more memorable and more popular, even when done in this slight subliminal fashion.

• They include them now simply as it is expected, and there is a game to find the messages when a new movie comes out.

• They generate extra publicity and any publicity is good publicity and raises the profile of the movie.

Signal detection theory

• Study of people’s tendencies to make correct judgments in detecting the presence of stimuli

• How well do your senses stack up?

Touch Threshold Experiment 1. Each pair will receive two toothpicks taped together. 2. One partner will close his or her eyes and the other partner will

LIGHTLY poke the him or her with one or both toothpicks.3. The partner being poked will report whether he or she felt one or

two points.4. Try this on various parts of the body (school appropriate!), like the

face, the forearm, the fingertip, the foot, etc.5. Record the body part tested and whether the subject guessed

correctly by creating a table on a half sheet of paper.6. Switch roles and run the experiment again. 7. Respond to this question at the end of the experiment. What does

this experiment tell us about the varying sensitivity of different areas of the body?

8. Everyone will turn in table showing the results of their partner and response to question.

Difference Thresholds

• The minimum difference between two stimuli required for detection 50% of the time

• Also known as… just noticeable difference

• Weber’s Law: two stimuli must differ by a constant minimum percentage for their difference to be perceptible

Objective 3: What is sensory adaptation?

• Sensory receptors lose their sensitivity in response to unchanging stimulus

Objective 3: How do we benefit from being unaware of unchanging stimuli?

• Enables us to focus on informative changes in our environment without being distracted by the uninformative constant stimulation of garments, odors, and street noise.

• Frees up our attention• **Television

“We need above all to know about changes; no one wants or needs to be reminded 16 hours a day that his shoes are on.”

-Neuroscientist David Hubel (1979)

Process p.24

• What types of sensory adaptation have you experienced in the last 24 hours?

Objective 4: What is transduction?

• Conversion of one form of energy to another. • Sensory systems encode stimulus energy as

neural messages– Eyes transduce (transform) light energy into neural

messages brain what you consciously see

Objective 4: What sort of energy does our visual system intake?

• Light = electromagnetic energy

Objective 5: What are the major structures of the eye?

• Pupil: the opening in the eye that allows light to enter

• Iris: a muscle that determines the amount of light that enters through the pupil; colored portion that constricts and expands

• Lens: located directly behind the pupil, bends the light wave, focusing it on the retina

• Retina: light sensitive inner surface located in the back of the eye; where transduction occurs

Objective 5: What are the major structures of the eye?

Objective 5: How do the structures of the eye guide incoming light toward receptor cells?

1. Light passes through cornea2. Light passes through pupil3. Lens bends the light wave to focus on retina– Accommodation refers to the process of how the lens

focuses in an out on images4. Retina contains photoreceptors (rods and cones)5. Greatest concentration of cones is on fovea6. Bipolar cells are specialized neurons that connects

rods and cones to ganglion cells7. Ganglion cells optic nerve which carries info to brain8. A blindspot occurs where optic nerve leaves retina

• Nearsightedness: nearby objects are seen more clearly than distant objects.

• Farsightedness: far away objects are seen more clearly than near objects

Objective 6: How does the retina react to light?

• Produces chemical changes that generate neural signals activate bipolar cells active ganglion cells

• Ganglion cells form the optic nerve which carries information to your brain

Objective 6: What are the differences between rods and cones?

• Rods– Active in dimly lit

conditions– Detect black, white, and

gray– Peripheral and twilight

vision

• Cones– Active in brightly-lit

conditions– Detect fine details and

color– Daylight vision– Cluster around fovea