Chapter 3 Sensing & Responding

Human Performance Engineering

Robert W. Bailey, Ph.D.

Third Edition

Responders

Sensors

Figure 4-1 Simplified model of human information processing with the sensors emphasized

Sensing is done by specialized

nerves called receptors.

Ex. Pain receptors- spread throughout

the body

Ex. Eyes- Concentrated in one location

Senses:Vision, Hearing, Smell, Taste, Touch

Cold, warmth, pain, kinesthetic (movement),vestibular (movement through space)

Sensing VS. Perception

Sensing is the capture and transformation

of information required for the

process of perception to take place.

Perception can be enhanced with experience.

Threshold - The point on an intensity scale below which we do not detect the stimulus and above which we do.

Difference threshold - The minimum physical difference that produces a perceptible difference.

Table 4.1 Various Forms of energy and the senses each stimulates

Stimuli SenseElectromagnetic VisionMechanical Hearing

TouchPainVestibularKinesthetic

Thermal ColdWarm

Chemical TasteSmell

(Adapted from Human Behavior: A System Approach. By N. W. Heimstra and V.S. Elingstad. Copyright ©1972 by Wadsworth Publishing Company, Inc. Reprinted by permission of the publisher. Brooks/Cole Publishing Company. Monterey, California.)

Table 4.2 Some Approximate Sensory Thresholds

Sense Detection Threshold

Sight Candle flame seen at 30 miles on a dark clear night

Hearing Tick of a watch under quiet conditions at 20 feet

Taste Teaspoon of sugar in 2 gallons of water

Smell Drop of perfume diffused into the entire volume of a three-room apartment

Touch Wing of a bee falling on your cheek from a distance of 1 centimeter

(Adapted from Galanter, 1962)

What is the most important sense?

Vision

The light that stimulates the eye is a form of electromagnetic radiation. The eye converts the light into a form that can be used by the brain.

The Sensity of the eye depends on:

Size of stimulus, brightness and contrast of the stimulus, size of visual field, region of retina stimulated

Common Visual Defects:

Hyperopic- Eyeball is shorter than normal

Myopic- Abnormally long eye ball

Night Blindness – Vitamin A deficiency

We will discuss only three of several visual deficiencies that could exist and that are correctable if recognized. Two of the most common correctable visual defects, hyperopic and myopia (nearsightedness), are usually due to shape abnormalities in the eyeballs. Figure 4-8 illustrates the structure of normal, hyperopic, and myopic eyes.

Normal: Light Focuses on the retina

Hyperopia: Light focuses in back of the retina for near objects

Myopia: Light focuses in front of the retina for far objects

What are two visual deficiencies not correctable?

Blindness & Color Blindness

(Red, Green, Gray)

8% of Men, 1% of Women

Hearing

19% of working-age Americans have a hearing impairmentFrequency – pitch, intensity – loudness

Sound Pressure Level (d8)

01020

3040

50607080

Threshold of hearing

Whisper

Quiet Office, Household sounds

Normal conversation

Average auto; loud radio

90Truck or bus

100

110

120130140

Subway train

Loud Thunder

Painful sound

Ear damage possible

Figure 4-10 Sound pressure levels for typical sounds

What are cutaneous senses?

Related to the Surface of the Body:

Touch (Pressure)-experienced when a depression is formed on the skin.

Pain- can motivate and deteriorate human performance more than any other stimulus.

Temperature – Cold & Warmth

Skin Temperature – 91.4 F

Taste- Sweet, Sour, Salty, & Bitter

Smell- 6 Qualities:Spicy, Fruity, Burnt, Resinous, Flowery, & Putrid 10,000 times as sensitive as taste

Kinesthetic (muscle sense) 3rd most important sense related to human performance. It provides information on: The position of the limbs,How far they have moved,The posture of the body as a whole.

Vestibular- Provides people with information about their position in a three – dimensional space and their movement through space. Located in the inner ear.

* Sensory adaptation & sensory interaction