Effects of Warning Validity and Proximity on Responses to

Warnings

Joachim Meyer, IsraelHUMAN FACTORS, Vol. 43, No. 4 (2001)

Introduction

• The ability to predict operators’ actions is crucial for the design of complex systems.

• Operators’ responses to such warnings are likely to change because of adaptive learning processes. People may learn to ignore frequent false alarms. (cry-wolf syndrome).

• People may learn to rely too strongly on a warning system and may ignore additional information, a phenomenon akin to misuse of automation or automation bias.

Signal Detection and Warnings

• In terms of signal detection theory, the use of a decision aid can be considered as the combined performance of two detectors: the operator and the warning system.

• In this paper I will consider a very simple system with binary output from the warning system and a binary response by the operator.

Proximity

• A more-salient warning that attracts attention may lead to a stronger response than a less-salient one.

• Low-proximity tasks require the separate consideration of variables, whereas high-proximity tasks require the integration of variables.

The aim of this experiment

• The experiment addressed participants’ use of warnings as a function of warning validity and proximity to the continuous information.

Method-participants

• Participants were 64 students in an ergonomics course who participated as part of a class assignment.

• Each was randomly assigned to one of the four experimental conditions.(2 warning validity*2 display)

• The experiment was conducted on PC 486 computers with 14-inch (36-cm) SVGA monitors.

• It showed an 8-cm gray square at the center of the screen. Above the square were two white fields, labeled “Last Trial” and “Score.”

Method-apparatus

• The experimental stimulus was a 0.5-cm wide rectangle.

• The height of the rectangle varied, and participants had to decide in each trial whether the rectangle was sampled from a distribution of long or short rectangles.

• In each trial the rectangle was drawn at a different position in the square field and remained visible for 1 s.

• Participants responded by pressing either the 6 or the 3 key on the numeric keypad.

• The next trial began after a 3-s delay.

Procedure and Design

• An experimental session consisted of five blocks, each with 100 trials. For 60 trials the stimuli were sampled from the short distribution, and for 40 trials they were sampled from the long distribution.

• The participants were told that longer rectangles tended to indicate failures.

• The warning had one of two forms (low and high proximity).

• Low proximity-separate display condition the warning appeared as a small rectangle that above the center of the field.

• High proximity-integrated display condition the warning appeared as the color of the continuous stimulus.

• The warning could be either red, indicating a possible malfunction, or green, indicating that there was no alert.

• 0 points for hits (correct identification of a signal) and for false alarms (responding “signal” when there actually was noise)

• 1 point for correct rejections (responding “noise” when there actually was no signal),

• lost 3 points for misses (responding “noise” when there was a signal).

Result and Discussion-Sensitivity of the Detector

• With valid warnings participants reached a maximal sensitivity that was lower than the sensitivity of the warning system.

• the warning appeared in the integrated display condition for a much shorter time than in the separate condition.

• With non-valid warnings the participants’ sensitivity was higher with separate displays than with integrated displays.

• Participants tended to take the warning indicators into account even when they were not valid.

• The valid warning condition showed neither an effect of the experimental block nor any interaction that involved the block.

Result and Discussion-The Cutoff Settings

• With non-valid warning, participants apparently learned to respond more cautiously when the warning was green, but they did not alter their response tendencies when the warning was red.

• When the warning was red, the integrated display led to clearly more cautious responses than did the separate display, whereas the cutoff settings for the two displays were the same for green warnings.

• Compliance- the operator’s responding as if there is actually a malfunction in the system when the system indicates the possibility of a malfunction.( 相當於紅燈警示 )

• Reliance- the operator assuming that the system is in a safe state when the indicators say so.( 相當於實驗中綠燈 )

Result and Discussion-Trust and Bias

• Experimental block affected the cutoff settings only when the indicator was green, whereas the display form affected only compliance.

• Automation Bias- Participants’ responses to non-valid warnings can be considered a form of overreliance.

Conclusions

• An operator’s reliance and compliance with a warning system are strongly situation dependent.

• The results show that the combination of warnings and human operators is not necessarily superior to the performance of the more sensitive system component alone.

• Warnings may be beneficial to place them in close proximity to other relevant information, but such a close positioning may make it more difficult to ignore irrelevant warning information.