1. PSYCHOLOGY (8th Edition) David Myers
PowerPoint Slides
Aneeq Ahmad
Henderson State University
Worth Publishers, © 2006

2. Sensation Chapter 5

3. Sensation & Perception
How do we construct our representations of the external world?
To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation.
When we select, organize, and interpret our sensations, the process is called perception.
OBJECTIVE 1| Contrast sensation and perception, and explain the difference between bottom-up and top-down processing.

4. Bottom-up Processing
Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind.
Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

5. THE CHT Top-Down Processing
Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations.
THE CHT

6. Making Sense of Complexity
Our sensory and perceptual processes work together to help us sort out complex images.
We start with sensory receptors and work up to higher levels of processing. Psychologists refer to sensory analysis that starts at the entry level as bottom-up processing. As this image illustrates, we construct perceptions drawing both on sensations coming bottom up to the brain, and on our experience and expectations, which psychologists call top down processing.
Our sensory and perceptual processes work together to help us sort out the complex images in this Bev Doolittle painting titled “The Forest Has Many Eyes”. Bottom up processing enables our sensory systems to detect lines, angles, and colors that form the horses, rider, and surroundings.
Using top-down processing we consider the paintings title, and then direct our attention to aspects of the painting that will give those observations meaning.
“The Forest Has Eyes,” Bev Doolittle

7. Failures in sensory processing:
:45
:16
Super-recognizer test:

8. Why might it be important to identify faces from an evolutionary standpoint?
Facial recognition is often an emotional experience for the brain and the amygdala is highly involved in the recognition process.
The eyes are often viewed as important features of facial expressions. Aspects such as blinking rate can be used to indicate whether or not a person is nervous or whether or not he or she is lying. Also, eye contact is considered an important aspect of interpersonal communication. However, there are cultural differences regarding the social propriety of maintaining eye contact or not.
The act of recognizing a face is actually quite complex. Like many visual stimuli, faces must be accurately recognized in any orientation or lighting condition, and even while moving. But unlike other objects, faces are intimately involved in communication, and our brains must be able to extract a tremendous amount of subtle detail from just a glance.

9. Sensing the World
Senses are nature’s gift that suit an organism’s needs. A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice.
Nature’s sensory gifts suit each recipient’s needs. They enable each organism to obtain the information it needs. Consider:
A frog, which feeds on flying insects, has eyes with receptor cells that fire only in response to small, dark, moving objects. A frog could starve to death knee-deep in motionless flies. But let one fly move by and the frog’s bug detectors cells snap awake.
A male silkworm moth has receptors so sensitive to the female sex-attractant odor that a single female need release only a billionth of an ounce per second to attract every male silkworm moth within a one-mile radius.
Humans are similarly designed to detect what are, for us, the important features of our environment. Our ears are most sensitive to sound frequencies that include human voice consonants and a baby’s cry.

10. Exploring the Senses
What stimuli cross our threshold for conscious awareness?
Could we be influenced by stimuli too weak (subliminal) to be perceived?
Why are we unaware of unchanging stimuli, like a band-aid on our skin?
Common questions people ask in the study of sensation.
What stimuli cross our threshold for conscious awareness?
Could we be influenced by stimuli too weak (subliminal) to be perceived?
Why are we unaware of unchanging stimuli, like a band-aid on our skin?

11. Psychophysics
A study of the relationship between physical characteristics of stimuli and our psychological experience with them.
Physical World
Psychological World
Light
Brightness
Sound
Volume
Pressure
Weight
Sugar
Sweet
We exist in a sea of energy. Even as we speak, we are being struck by x-rays and radio waves, ultraviolet and infrared light, and sound waves of very high and very low frequency. To all of these, we are blind and deaf. Other animals detect the world that lies beyond the human experience. Birds use a magnetic compass. Bats and dolphins locate prey with the use of sonar. The shades of our own senses are open just a crack, allowing us only a restricted awareness of this vast sea of energy. Psychophysics is the study of how this energy relates to our physical experience.

12. Detection Absolute Threshold Intensity No No No Yes Yes Detected
We can sense very faint stimuli. For example, we can feel a bees wing fall on our cheek. If we were standing on top of a mountain on a dark clear night, we could see a candle flame 30 feet away. We could smell a single drop of perfume in a three-room apartment.
Our awareness of these faint stimuli illustrates our absolute thresholds, which is the minimum stimulation necessary to detect a particular light, sound, pressure, taste, or odor 50 percent of the time. No No No
Yes
Yes
Observer’s Response
Detected
Tell when you (the observer) detect the light.

13. Thresholds
Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time.
Proportion of “Yes” Responses
Stimulus Intensity (lumens)
OBJECTIVE 2| Distinguish between absolute and difference thresholds, and discuss whether we can sense stimuli below our absolute thresholds and be influenced by them.

14. Subliminal Threshold
Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness.
Can we be affected by stimuli so weak as to go unnoticed? Under certain circumstances, the answer is yes. An invisible image or word can prime your response to later questions. In a typical experiment, the image or word is quickly flashed, then replaced by a masking stimulus that interrupts the brains processing before conscious perception. For example, one experiment subliminally flashed either positive scenes, (kittens, a romantic couple) or negative scenes (a werewolf, a dead body), an instant before participants viewed slides of people. Although the participants consciously perceived only a flash of light, they gave more positives ratings to people whose photos had been associated with the positive scenes. People somehow looked nicer if their photo immediately followed unperceived kittens, rather than an unperceived werewolf. This experiment illustrates an intriguing aspect of the priming effect: sometimes we feel what w do not know and cannot describe.
Anything that happens in the 50% response rate or below is said to be subliminal (as that is what the word subliminal means- sub (below) the line.
Kurt Scholz/ Superstock

15. Subliminal Messages- Do they actually work?
A study was conducted by Anthony Greenwald to determine the effectiveness of subliminal messages as it pertained to self-help tapes. Participants were either given a self-help tape on memory or self-esteem, however, on half of the tapes, the title of the tape was switched, meaning that some people got a tape with subliminal messages about memory, with a title suggesting it was a self help tape on self-esteem.
5 weeks later, participants were assessed to determine the effectiveness of the subliminal messages. Every person who received a tape regarding the improvement of memory reported that they had a better regardless of the fact that some of the memory tapes were actually about self- esteem. So it was for the self-esteem participants. They all reported higher self-esteem, even though half of them got tapes about memory.
Over a decade, Greenwald continued to conduct double-blind experiments evaluating subliminal self-help tapes. His results were uniform: not one had any therapeutic effect. His conclusion is that subliminal procedures offer little or nothing of value to the marketing practitioner.

16. Difference Threshold
Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND).
Difference
Threshold
To function effectively, we need absolute thresholds low enough to detect important sights, sounds, textures, tastes and smells. We also need to detect small differences among stimuli. For example- A wine taster must be able to detect the slight flavor difference between two vintage wines. Parents must detect the sound of their own child’s voice amid other children's voices. No No
Yes
Observer’s Response
Tell when you (observer) detect a difference in the light.

17. Weber’s Law
Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I.
Stimulus
Constant (k)
Light 8%
Weight 2%
Tone 3%