summary (B)

It speaks about the reaction time, which is decomposed to:

1_Mental processing time :

Which is the time taken for a person to receive a signal to do some thing and this it self-decomposited to 4 stages?

Ex:

When a driver sees some one walking and has to stop.

*Sensation.

*Recognition.

*Situation awareness.

*Response selection and programming.

2_Movement time:

Is the time taken to do the response?

Ex: The time taken to put the foot on the brake.

3_Device response time :

Which will take the time for the car to stop and this will not happen immediately.

*Total stopping distance constant of 3 components.

a) Reaction distance.

We will calculate it on the following the reaction time is 1.5 second, so the car will move 1.5x80.67 or 120.9 feet before stopping.

b) Brake engagement.

Which is the longest reaction, it is variable.

c) Physical force distance.

Is determining the brake engage by physical force, which is 134.4 feet.

So total stopping distance:

120.9ft+24.2 ft+134.4ft=279.5ft

4_Expectation:

The time for reaction is affected by if the driver is alerted to need the brake.

We divide alerted into three classes.

*Expected: take 0.1 second in this case the driver is aware.

*Unexpected: takes 1.25 which may happened for a driver before red signal .

*Surprise: the best estimate is 1.5 second happened in unusual circumstance.

*Urgency: brake happens faster in urgency.

*Cognitive load: will take from 0.3 à1 second.

*Stimulus _Response Compatibility:

Is calculating the thing in a short time.

*Psychological Refractory Period:

New responses are made slower than first responses.

5_Age:

Old people have more experience and tendency from others, and the researches say that older people respond slower than younger.

Gender: female respond slower than males.

Nature of signals:

_First difficult situation is acceleration or decleration motion of car.

Difficult to judge a motion toward or away from you .

_Second it is not easy to judge a motion of an object if you are moving.

_Third it is much slower when people encounter a law probability or unexpected.

6_Visibility:

The reaction will be decreased in bad visibility.

in good light the reaction will be better and faster .

7_Response Complexity:

The moving for turning a wheel is faster than to step on the brake this returns to that complex muscular response takes longer time.

8_reaction time at night:

Low contrast and low conspicuity at night can give faster reaction.

9_Case study:

A 73 years old male driver was driving his car near an intersection and he saw a car coming from other side so he had to put his foot on the brake.

_What is his expected reaction time?

*To get the alert that an accident might happen will take 1.0 to 1.1 second.

*The time to move his foot is 0.2 second.

*His 73 age will increase expected reaction to range 1.1-1.3 second.

10_Complex reaction time :

Donders distinguish 3 type of reaction time:

A_B and C.

Final comments:

This takes about that each reaction time has its peculiarities and must be examined.