ISO 17488:2016

INTERNATIONAL ISO
STANDARD 17488
First edition
2016-10-01
Road vehicles — Transport
information and control systems
— Detection-response task (DRT)
for assessing attentional effects of
cognitive load in driving
Véhicules routiers — Systèmes d’Information et de commande du
transport — Tâche de Détection-Réponse (DRT) pour l’évaluation des
effets attentionnels de la charge cognitive lors de la conduite
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Abbreviated terms . 5
5 DRT methodology: Principles and overview . 5
6 Measurement methods and procedures . 6
6.1 Participants . 6
6.2 Experimental setup . 6
6.2.1 Non-driving experimental setup . 6
6.2.2 Surrogate driving experimental setup . 6
6.2.3 Driving simulator experimental setup . 6
6.2.4 On-road experimental setup . 6
6.3 Stimulus presentation. 6
6.3.1 Stimulus presentation timing . 7
6.3.2 Visual stimulus specifications . 8
6.4 Response method .10
6.5 Primary driving task .11
6.6 Instructions to participants .11
6.7 Training procedure .11
6.7.1 Secondary task training .12
6.7.2 DRT training .12
6.7.3 Primary task training .12
6.7.4 Training on multitasking .12
6.8 Performance measures .12
6.9 Analysing and interpreting DRT performance data .13
6.10 Checking data quality .13
6.11 Use of DRT data in decision making .14
Annex A (normative) Rationale .15
Annex B (normative) Guidelines for selecting between variants of the DRT method .23
Annex C (normative) Additional factors affecting DRT performance .25
Annex D (informative) DRT variants .27
Annex E (informative) Summary of results from the ISO-coordinated studies .38
Bibliography .69
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 22, Road vehicles, Subcommittee SC 39,
Ergonomics.
iv © ISO 2016 – All rights reserved

Introduction
Driving is a complex task consisting of a range of sub-tasks such as keeping the vehicle in the lane,
avoiding other traffic and obstacles, observing road signs and signals, planning and initiating specific
manoeuvres, scanning mirrors and navigating. In addition, drivers often engage in secondary tasks, not
directly related to driving, such as operating the media player, conversing on the phone and reading
road-side commercial signs.
These different activities place varying, and sometimes conflicting, demands on the driver. In order to
manage the various driving and secondary tasks, the driver thus needs to allocate different resources,
such as the eyes, hands, feet, perceptual systems, motor control systems and higher level cognitive
functions, to the different sub-tasks in a dynamic and flexible way. This allocation of resources to
driving and non-driving activities may be generally conceptualized as driver attention. In most driving
situations, attention is determined by an interaction of proactive (top-down, endogenous) processes
based on anticipation of how the upcoming situation will develop and bottom-up processes (driven by
exogenous stimuli) which can trigger attention to the situation when it does not develop as expected,
even leading to a corrective action.
There is a need for methods that can be used to assess how engagement in secondary tasks affects driver
attention. In general, the effect of a task on attention depends on the amount and type of resources
demanded by the task. As outlined in further detail in Annex A, resources can be conceptualized at
three general levels: sensory-actuator resources, perceptual-motor resources and cognitive resources.
Sensory/actuator resources refer to the basic interfaces between the driver and the environment used
to sense the environment and perform overt actions. Examples include the eyes, the ears, the skin, the
feet, the hands, the mouth, the vocal cords, etc. Perceptual/motor resources can be regarded as brain
functions for controlling specific perceptual-motor activities, e.g. visual perception, manual tracking
and hand-to-eye coordination. Finally, cognitive resources refer to brain systems implementing higher-
level cognitive operations such as planning, decision making, error detection, sustaining information
in working memory, dealing with novel or difficult situations and overcoming habitual actions. These
types of high-level cognitive functions may be conceptualized in terms of cognitive control. While
sensory-actuator and perceptual-motor resources are, at least to some extent, modality-specific,
cognitive control can be regarded as a single resource with strongly limited capacity, not associated
with any particular sensory modality. Cognitive load thus refers specifically to the demand for cognitive
control that a task imposes on the driver.
Several existing and draft ISO standards address the assessment of secondary task demand in the
[1] [2]
context of driving. ISO 15007-1 and ISO/TS 15007-2 provide guidance on how to measure glance
[3]
behaviour and ISO 16673 focuses exclusively on the viewing time required to perform a task using an
in-vehicle information system. Hence, these methods focus mainly on the assessment of (visual) sensory
[4]
demand (i.e. the demand for the eyes). ISO 26022 provides a technique for evaluating the combined
effect of sensory-actuator, perceptual-motor and cognitive demands on a driver’s performance in a
combined event detection and vehicle control task.
However, a standardized measurement method that specifically addresses cognitive load is lacking.
While, for example, ISO 26022 is sensitive to cognitive load, it lacks specificity since its main
performance metric (MDEV) is also sensitive to visual sensory motor interference (i.e. visual time
sharing; see Annex A). A standardized method specifically addressing cognitive load is particularly
needed in order to evaluate the attentional demands of new driver-vehicle interfaces designed to
minimize visual interaction such as voice-based interfaces, haptic input devices and head-up displays.
The detection-response task (DRT) method defined in this document intends to fill this gap. More
specifically, the DRT is mainly intended to measure effects of the cognitive load of a secondary task on
attention. However, some versions of the DRT specified in this document may also be used to capture
other forms of secondary task demand (e.g. visual sensory demand). The general rationale behind the
DRT methodology is further outlined in Annex A.
Annex B provides guidance on how to select among the different DRT versions defined in this
document. Annex C reviews factors that could potentially affect DRT performance and thus need to be
accounted for when designing DRT experiments. Annex D offers a review of existing alternative DRT
methodologies not covered by this document. Annex E provides an overview of the results from a set of
coordinated studies with the purpose to support the development of this document. Finally, a general
bibliography is provided for existing DRT-related research.
vi © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 17488:2016(E)
Road vehicles — Transport information and control
systems — Detection-response task (DRT) for assessing
attentional effects of cognitive load in driving
1 Scope
This document provides a detection-response task mainly intended for assessing the attentional effects
of cognitive load on attention for secondary tasks involving interaction with visual-manual, voice-
based or haptic interfaces. Although this document focuses on the assessment of attentional effects of
cognitive load (see Annex A), other effects of secondary task load may be captured by specific versions of
the DRT, as further outlined in Annex B. Secondary tasks are those that may be performed while driving
but are not concerned with the momentary real-time control of the vehicle (such as operating the media
player, conversing on the phone, reading road-side commercial signs and entering a destination on the
navigation system).
NOTE According to this definition, secondary tasks can still be driving-related (such as in the case of
destination entry).
This document does not apply to the measurement of primary (driving) task demands related to
the momentary real-time control of the vehicle, such as maintaining lane position and headway or
responding to forward collision warnings. However, this does not preclude that the DRT method, as
specified in this document, may be adapted to measure such effects.
This document applies to both original equipment manufacturer (OEM) and after-market in-vehicle
systems and to permanently installed, as well as portable, systems.
It is emphasized that, while the DRT methodology defined in this document is intended to measure the
attentional effects of cognitive load, it does not imply a direct relationship between such effects and
crash risk. For example, taking the eyes off the road for several seconds in order to watch a pedestrian
may not be very cognitively loading but could still be expected to strongly increase crash risk.
Furthermore, interpret DRT results cautiously in terms of demands on a specific resource, such as
cognitive load. Specifically, if the goal is to isolate the effect related to the cognitive load imposed by a
secondary task on attention, avoid overlap with other resources required by the DRT (e.g. perceptual,
motor, sensory or actuator resources). A particular concern derives from the fact that the DRT utilizes
manual responses (button presses). Thus, for secondary tasks with very frequent manual inputs (on
the order of one or more inputs per second), increased response times on the DRT may reflect this
specific response conflict (which is due to the nature of the DRT) rather than the actual cognitive
load demanded by the task when performed without the DRT (i.e. alone or during normal driving;
see Annex E). Thus, for such response-intensive tasks, DRT results are interpreted with caution. This
document defines three versions of the DRT and the choice of version depends critically on the purpose
of the study and the conditions under which it is conducted (see Annexes A and B for further guidance
on this topic).
This document specifically aims to specify the detection-response task and the associated measurement
procedures. Thus, in order to be applicable to a wide range of experimental situations, this document
does not define specific experimental protocols or methods for statistical analysis. However, some
guidance, as well as examples of established practice in applying the DRT, can be found both in the main
body of this document and in the annexes (in particular Annexes C and E).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
actuator demand
demand for actuator resources (3.2) imposed by a task (3.30)
3.2
actuator resources
human body systems used to execute overt motor actions
Note 1 to entry: Examples of actuator resources include the hands, the feet, the vocal cords, etc.
3.3
attention
allocation of resources, encompassing both bottom up and top down attentional processes, to a
particular activity or activities
3.4
cognitive control
mental operations such as planning, decision making, error detection, inhibiting habitual actions,
utilizing information in working memory (3.36), and resolving novel and complex situations
3.5
cognitive resources
brain systems implementing cognitive control (3.4)
3.6
cognitive load
cognitive demand
demand for cognitive control (3.4) imposed by a task (3.30)
3.7
data segment
continuous portion of data
3.8
driver attention
allocation of resources (3.20), encompassing both bottom up and top down attentional processes, to
driving and/or non-driving-related activities
3.9
DRT stimulus
sensory signal controlled and issued to a participant during a DRT test session for the purpose of
eliciting a specified response (3.21)
3.10
hit
response (3.21) initiated within 100 ms to 2 500 ms from the stimulus onset (3.29), not preceded by an
earlier response in the same interval
Note 1 to entry: Hit is synonymous with valid response.
2 © ISO 2016 – All rights reserved

3.11
hit rate
number of valid responses (3.33) divided by the total number of stimuli presented in a data collection
segment, excluding premature responses to stimuli
Note 1 to entry: See premature response (3.17).
3.12
missing response
absence of a response (3.21) within 100 ms to 2 500 ms after stimulus onset (3.29)
3.13
motor demand
demand for motor resources (3.13) imposed by a task (3.30)
3.14
motor resources
brain systems implementing the control of motor actions
3.15
perceptual demand
demand on perceptual resources (3.15) imposed by a task (3.30)
3.16
perceptual resources
brain systems implementing perception
Note 1 to entry: Perceptual functions include lower-level, modality-specific perception (e.g. visual and auditory
perception), as well as higher-level cross-modal perceptual integration.
3.17
premature response
response (3.21) initiated within 100 ms from the stimulus onset (3.29), prior to the timing interval for a
valid response (3.33)
3.18
primary task
driving or driving-like task (3.30) used in the surrogate driving, driving simulator or on-road DRT
experimental setups
3.19
repeated response
response (3.21) initiated within 100 ms to 2 500 ms after the stimulus onset (3.29) that is preceded by
an earlier response in the same interval
3.20
resources
systems in the brain or body that can be utilized to perform tasks (3.30)
3.21
response
signal generated by the participant pressing the response button
3.22
response time
time from the stimulus onset (3.29) until the response onset
Note 1 to entry: Response time is only defined for valid responses.
3.23
secondary task
task (3.30) that may be performed while driving but that is not concerned with the momentary real-
time control of the vehicle
Note 1 to entry: Examples include operating the media player, conversing on the phone, reading road-side
commercial signs and entering a destination on the navigation system. Thus, secondary tasks may be driving-
related.
3.24
sensory demand
demand on sensory resources (3.24) imposed by a task (3.30)
3.25
sensory resources
human body systems used to sense the exterior environment or internal bodily states
Note 1 to entry: Examples of sensory resources include the eyes, the ears, the skin, etc.
3.26
stimulus duration
time during which the stimulus is turned on
Note 1 to entry: The maximum stimulus duration is set at 1 s.
Note 2 to entry: Stimulus duration depends on responses. The maximum stimulus duration represents the pre-
set duration of the stimulus in the absence of a response. If the response is initiated prior to maximum stimulus
duration, the stimulus is turned off.
3.27
stimulus cycle period
time from the onset of a stimulus until the onset of the next stimulus
3.28
stimulus offset
point in time when the DRT stimulus (3.9) is turned off
3.29
stimulus onset
point in time when the DRT stimulus (3.9) is turned on
3.30
task
process of achieving a specific and measurable goal using a prescribed method
3.31
trial
test of one participant undertaking one secondary task (3.23) one time
3.32
unrequested response
response (3.21) given later than 2 500 ms after the stimulus onset (3.29)
3.33
valid response
response (3.21) initiated within 100 ms to 2 500 ms from the stimulus onset (3.29), not preceded by an
earlier response in the same interval
Note 1 to entry: Valid response is synonymous with hit.
4 © ISO 2016 – All rights reserved

3.34
visual angle
angle subtended at the eye by a viewed object or separation between viewed objects
Note 1 to entry: Measurement of visual angle is made edge to edge.
3.35
visual eccentricity
visual angle (3.34), relative to the centre of the fovea, at which a certain visual stimulus impinges on
the retina
Note 1 to entry: Measurement of visual eccentricity is made from centre of eye to centre of visual stimulus.
3.36
working memory
executive and attentional aspect of short-term memory involved in the interim integration, processing,
disposal and retrieval of information
4 Abbreviated terms
ANOVA analysis of variance
B baseline
DRT detection-response task
HDRT head-mounted DRT
HR hit rate
MR miss rate
N0 0-Back
N1 1-Back
OEM original equipment manufacturer
R response
RT response time
RDRT remote DRT
SE easy SuRT
SH hard SuRT
TDRT tactile DRT
5 DRT methodology: Principles and overview
The DRT method is based on a simple detection-response task where participants respond to relatively
frequent artificial stimuli presented with a specified degree of temporal uncertainty. Detection
performance, measured in terms of response time and hit rate, is assumed to represent the degree to
which attention is affected by the demand and, in particular, the cognitive load component imposed
by the secondary task under evaluation. Longer reaction times and reduced hit rate are indicative of
higher cognitive load.
The method may be implemented in several different ways, depending on the purpose of the study.
The DRT versions specified by this document differ in terms of stimulus presentation modality and
experimental setup, as further described below.
6 Measurement methods and procedures
6.1 Participants
Participants should be licensed drivers with a similar level of prior experience with the secondary task
under evaluation. Other relevant characteristics of the participants shall be recorded, including at least
driving experience (e.g. miles or km driven in the last year), similar device use experience, gender, age
and previous experience with the DRT.
6.2 Experimental setup
The DRT may be used in different experimental setups as described below.
6.2.1 Non-driving experimental setup
In this setup, the DRT is performed concurrently with the secondary task under evaluation in a non-
driving situation. This means that attention is divided between the secondary task under evaluation
and the DRT, without simultaneous performance of a primary (driving or driving-like) task. DRT
performance with the secondary task is assessed relative to a baseline condition where only the DRT
is performed. The non-driving version of the DRT may be used to assess how a secondary task affects
selective attention in any non-driving setting, including production vehicles, vehicle mock-ups or at a
desktop.
6.2.2 Surrogate driving experimental setup
In this setup, the DRT is performed concurrently with the secondary task under evaluation while the
participant performs a surrogate task that functions as the primary task of driving. This surrogate
task could be a simple tracking task, watching a video of real-world driving recorded from the driver’s
viewpoint or a combination of such elements. DRT performance during the combined secondary task
and surrogate driving is assessed relative to a baseline condition where the DRT is performed with only
the surrogate driving task.
6.2.3 Driving simulator experimental setup
In this setup, the DRT is performed concurrently with the secondary task under evaluation while the
participant drives a driving simulator. DRT performance during the combined secondary task and
simulator driving is assessed relative to a baseline condition where the DRT is performed while only
driving the simulator. The same scenario is used in both conditions.
6.2.4 On-road experimental setup
In this setup, the DRT is performed concurrently with the secondary task under evaluation while the
participant drives on a closed track or an open road with traffic. Appropriate safety concerns shall be
addressed for on-road testing. DRT performance during the combined secondary task and driving is
assessed relative to a baseline condition where the DRT is performed while only driving.
6.3 Stimulus presentation
This document specifies three alternative methods for presenting the DRT stimulus. This includes two
methods where the stimulus is presented visually and one method where the stimulus is provided by
means of tactile stimulation. In the head-mounted DRT (HDRT), a visual stimulus (an LED) is presented
through a fixture attached to the head of the participant at a specified visual angle. In the remote
DRT (RDRT), a visual stimulus (e.g. an LED or embedded graphic in simulator scenario) is presented
6 © ISO 2016 – All rights reserved

in the forward view of the participant. Finally, in the tactile DRT (TDRT), a tactile vibrator is placed
on the participant’s body. These stimulus presentation methods are described in further detail below.
Guidelines for the selection of stimulus presentation mode depend on the purpose of the experiment
and are provided in Annex B.
6.3.1 Stimulus presentation timing
The stimulus presentation timing is the same for all three stimulus presentation methods. Figures 1
and 2 illustrate the key principles. The stimulus onset (S ) represents when the stimulus is turned on
on
and the stimulus offset (S ) when it is turned off. The stimulus duration (SD) represents the time during
off
which the stimulus is turned on and the maximum stimulus duration (SD ) represents the pre-set
max
maximum duration of the stimulus. SD should be set to 1 s. The stimulus cycle period (SCP) represents
max
the time from the onset of one stimulus until the onset of the next stimulus. The stimulus cycle period
shall vary and be drawn randomly from a uniform distribution of values between 3 s and 5 s.
Key
S stimulus onset
on
S stimulus offset
off
SD stimulus duration
SCP stimulus cycle period
Figure 1 — Definition of parameters relevant for stimulus presentation specification
A signal generated by the participant pressing the response button is referred to as a response (R). If
the participant responds while the stimulus is turned on, the stimulus is turned off at the moment of
response (see Figure 2).
Key
S stimulus onset
on
S stimulus offset
off
SD stimulus duration
SD maximum stimulus duration
max
R response
Figure 2 — Illustration of how the stimulus duration is determined by the response (R)
6.3.2 Visual stimulus specifications
6.3.2.1 Head-mounted visual stimulus
In the head-mounted DRT, the visual stimulus shall be presented by means of a single LED presented
on a stalk attached to the participant’s head. Compared with the remote DRT, the head-mounted DRT
has the main advantage that it is not affected by drivers’ head motion or if drivers look away from the
forward view. Figure 3 shows the setup for the head-mounted DRT. The LED should be supported by
a black frame as shown in Figure 3 and should be positioned to the left if the vehicle has the steering
wheel to the left and to the right for vehicles with the steering wheel to the right. For a non-driving
experimental setup, the LED should be placed either to the left or right, but in a way that visual
interference with the secondary task is minimized. More precisely, the LED should be positioned 20° to
the left or right (depending on steering wheel position) along the horizontal meridian and 10° above the
vertical meridian, using the left or right eye as reference point, as illustrated in Figure 3. The distance
between the eye closest to the LED and the LED should be 12 cm to 13 cm. The position of the LED
should be verified on a human or manikin head prior to beginning the experimental trials. However, it
does not have to be measured individually for each subject. Recommended default specifications for the
LED are given in Table 1. The luminous intensity of the LED should be adjusted to the lighting conditions
in the experimental setup so that the visual stimulus is easily detectable while not inducing discomfort
or harm to the participant.
Table 1 — Recommended specifications for the LED for the head-mounted DRT
Parameter Value
Colour Red
Dominant wavelength 626 nm
LED response time 90 ns
Diameter 5 mm
Maximum luminous 0,055 cd
intensity
Care should be taken to ensure that no portion of the LED is in the blind spot of the left eye. This can be
ensured by covering the right eye (when the LED is positioned to the left) and asking the test subject
to fixate straight ahead with the left eye. The entire LED (when continuously on) should then be clearly
visible in the peripheral visual field of the left eye (when the LED is positioned to the right, the reverse
applies).
8 © ISO 2016 – All rights reserved

Figure 3 — Illustration of the setup for the head-mounted DRT
6.3.2.2 Remote visual stimulus
The stimulus for the remote DRT can be implemented as a single LED or, in driving simulator setups,
as a graphical object displayed in a fixed location in the visual display. If an LED is used to generate
the stimuli, it should be placed remotely from the participant, and should be clearly perceptible when
gaze is directed straight towards the forward roadway. The LED should be directly perceived by the
driver (i.e. not only indirectly perceived, for example, through reflection in the windshield). The exact
positioning of the LED depends on the experimental setup. For example, in a passenger vehicle or
simulator mock-up, the top of the dashboard would be a suitable position for the LED, as long as it is not
occluded by the steering wheel. In outdoor conditions, care should be taken to find a position where the
influence of ambient lighting on stimulus visibility is minimized (e.g. by means of shielding).
Recommended default specifications for the LED are given in Table 2. The luminous intensity of the LED
should be adjusted to the lighting conditions in the experimental setup so that the visual stimulus is
easily detectable while not inducing discomfort or visual impairment to the participant.
Table 2 — Recommended specifications for the LED for the remote DRT
Parameter Value
Colour Red
Dominant wavelength 626 nm
LED response time 90 ns
Diameter 5 mm (placed at a distance
that subtends approximately
1°)
Image luminance 2 cd/m2
The exact position of the RDRT stimulus (distance from the participant, visual angle, etc.) shall be
reported in each experiment. If the stimulus is presented graphically on a visual display, the stimulus
should be implemented as a red filled circle, subtending a visual angle of about 1°. The stimulus should
be presented within the driver’s central field of view in a fixed location on the screen.
6.3.2.3 Tactile stimulus specification
A small electrical vibrator (tactor) is used to present the stimulus for the tactile DRT. The tactor
should be placed on the driver’s left shoulder if the vehicle has the steering wheel on the left and the
opposite shoulder for vehicles with the steering wheel on the right. For a non-driving experimental
setup, the tactor can be placed on either side. The tactor may be attached using medical tape, as
illustrated in Figure 4. The intensity of the tactor should be such that it is easily detectable while not
inducing discomfort to the participant. This should also include consideration for vibrations in the test
environment such as vehicle vibration for on-road setup. Caution should be taken to avoid interference
with the seat belt when it is fastened. The technical specifications of the tactor should be documented
since the characteristics of the tactor (type, frequency and acceleration) may influence reaction time.
Recommended default specifications for the tactor are given in Table 3.
Table 3 — Recommended specifications for the tactor
Parameter Value
Diameter 10 mm
Weight 1,2 g
Maximum speed 12 000 rpm
Vibration amplitude 0,8 G
Figure 4 — Placement and attachment of the tactor
6.4 Response method
For all versions of the DRT, participants respond by pressing a micro-switch. It can be attached to the
index finger, the middle finger or the thumb, as chosen by the participant, but placement should remain
consistent throughout testing. The micro-switch should be attached to the participant’s left hand if the
vehicle has the steering wheel on the left and to their right hand for vehicles with the steering wheel on
the right. An example is illustrated in Figure 5.
The micro-switch should generate a binary signal representing the response signal in Figure 2. In
experimental setups involving driving, or a surrogate for driving involving the use of the steering
wheel, the response should be made by pressing the switch to the steering wheel. In non-driving
10 © ISO 2016 – All rights reserved

experimental setups, the micro-switch should be pressed against the thumb or the desktop (as chosen
by the participant). The micro-switch shall provide perceptible feedback clearly indicating that a
response has been made.
Figure 5 — Illustration of the setup for the response micro-switch
6.5 Primary driving task
If the DRT is used in a surrogate driving, driving simulator or on-road experimental setup, the nature of
the primary task shall be clearly reported. Factors that should be considered are provided in Annex C.
6.6 Instructions to participants
At a minimum, the following instructions should be given to participants before training on the
different tasks.
a) Welcome the participant and give a brief overview of the purpose of the test, its expected duration
and the test procedure.
b) Emphasize that the intention is not to test participant skills but rather how different tasks might
affect performance.
c) Explain the secondary task to be evaluated, the general principles behind the DRT and the primary
task (if applied in a surrogate driving, driving simulator or on-road experimental setup). The
participant should be instructed to prioritize the primary task (driving or a surrogate for driving)
and then, as a lower priority, do their best to also perform both the secondary task under evaluation
and the DRT. In the non-driving experimental setup, the participant should be instructed to do
their best to perform both the secondary task under evaluation and the DRT simultaneously. The
following is an example of a task priority instruction suitable for an experimental setup involving
driving: “Your main priority is to drive safely. Please remember to maintain your position within
your given travel lane. The [LED/tactor] and the [secondary task] task will both be active during
the run. Please do your best to pay attention to both tasks but recall that your primary task is safe
driving.”
d) Explain to the participant that the data collection and analysis programmes are designed to ignore
participant responses that are given when there is no stimulus presented. Thus, a strategy of
performing continuous button pressing regardless of stimulus presentation will not yield better
performance and shall lead the participant to be excluded from the experiment.
6.7 Training procedure
Prior to the experimental tests, the participant shall be separately trained on the following tasks in the
following order:
a) the secondary task(s) under evaluation;
b) the DRT;
c) if a surrogate driving, driving simulator or on-road experimental setup is used, the primary
(driving or driving-like) task.
Finally, the two or three tasks should be practiced together. The detailed training procedure is specified
in the following sections.
6.7.1 Secondary task training
Training on the secondary tasks shall initially be performed under single task conditions. A
demonstration of the task shall first be given to the participant by the experimenter. Participants shall
then be given a sufficient number of practice trials for each secondary task being investigated until they
reach stable performance and feel comfortable that they can perform the task successfully. If three out
of the first four participants cannot successfully complete the practice task at least once in five trials,
the interface design and training protocol should be reviewed.
The number of practice trials shall be recorded for each participant and task for post-test analysis.
Information to be viewed or entered for a secondary task in practice trials should be different from
those used in test trials but equal in complexity (e.g. street name length in a destination entry task).
Each practice task should be completed using the designated method and the experimenter should
aim to ensure the appropriate completion of the task by coaching or assisting if the participant is
having difficulty with the task. Care should be taken to ensure that the participant understands the
instructions.
6.7.2 DRT training
When the secondary task training is completed, the participant shall be trained on performing the
DRT (without performing the secondary or driving tasks). The training shall continue until the
subject responds to the stimuli in a stable manner (as judged by the experimenter) and reports feeling
comfortable with performing the task. The experimenter is advised to observe the participant during
the entire training phase to ensure that the participant attempts to respond as quickly as possible to
the DRT stimulus. If admonishing a subject who is not responding as quickly as he/she could do fails
to modify their behaviour accordingly, the subject should be eliminated from the test programme.
In addition, the experimenter should check that the participant does not simply press the button
repeatedly without consideration of the stimuli.
6.7.3 Primary task training
If the surrogate driving, driving simulator or on-road experimental setup is used, the participants shall
also be trained on the primary task (without performing the secondary task or the DRT). Training on the
primary task should continue until stable performance is achieved and the participant feels comfortable
with the task. Test participants who are apparently incapable of mastering the primary task, or who
complain of motion sickness during training, should be eliminated from the test programme.
6.7.4 Training on multitasking
Finally, the participants shall be trained on performing the secondary tasks together with the DRT
and the surrogate driving, driving simulator or on-road experimental setup, if used. In studies where
several secondary tasks are to be evaluated, the multitasking condition shall be practiced for each. The
training shall continue until stable multitasking performance is achieved and the participant reports
feeling comfortable with performing the two or three tasks simultaneously. Participants who are
clearly incapable of mastering the multitasking should be eliminated from the test, and this number
shall be documented along with the reasons for their exclusion.
6.8 Performance measures
Two performance measures shall be calculated: hit rate and response time. A hit is defined as a valid
response to a DRT stimulus. A valid response is defined as a response initiated within 100 ms to
12 © ISO 2016 – All rights reserved

2 500 ms from the stimulus onset, and which is not preceded by an earlier response in the same interval.
Responses can be categorized as valid or invalid. There are three general types of invalid responses, all
of which shall be excluded from the calculation of hit rate.
a) Premature responses: Responses initiated within 100 ms from stimulus onset, prior to the timing
interval for a valid respons
...