Camilli HFES-EC 2009

A short segment approach to cardiovascular

and ocular responses to task events and

mental workload changes

Marco Camilli, Arjan Stuiver, Willem Takens,

Francesco Di Nocera & Ben Mulder

Department of Psychology University of Rome "La Sapienza”, Italy

Department of Experimental Psychology, University of Groningen, The Netherlands

Background: Cardiovascular response [HR]

HRV (beat-to beat variations in interbeat interval)

decreases as mental effort increases. (e.g. Boucsein & Backs, 2000; De Rivecourt, et al., 2008)

Heart rate (HR) increases with an increase in mental effort.

(e.g. Roscoe ,1992; Wilson, 2001)

Background: Cardiovascular response [HRV]

HR spectrum - heart rate variability (HRV): low-frequency band (0.02–0.06 Hz) mid-frequency band (0.07–0.14 Hz) high-frequency band (0.15–0.40 Hz)

Mid-frequency band is most consistently related to

mental effort. (Mulder, 1985)

Background: Ocular response

Spatial distribution of eye fixations (by Nearest Neighbor Index: NNI)

Visual exploration pattern (fixations dispersion) is sensitive to mental workload changes.

(Di Nocera et al., 2006; Fidopiastis et al., 2009)

Fluctuating values by time series analysis. (Di Nocera et al., 2007)

Sensitivity to different types of task demand: visuo-spatial [éWLêNNI] vs. temporal [éWLéNNI].

(Camilli et al., 2008)

Camilli, M., Nacchia, R., Terenzi, M., & Di Nocera, F. (2008). ASTEF: A Simple Tool for Examining Fixations. Behavior Research Methods, 40(2), 373-382.

A Simple Tool for Examining Fixations

(ASTEF)

Objectives

Can HR(V) and NNI detect momentary

changes in mental effort, related to

specific task events in demanding and

less demanding conditions?

Ambulance dispatcher’s task [A1 call]

Ambulance dispatcher’s task [A1 activation]

Ambulance dispatcher’s task [A1 ride]

Ambulance dispatcher’s task [A3 call]

Ambulance dispatcher’s task [A3 scheduling]

Ambulance dispatcher’s task [A3 ride]

Method: task load conditions

Easy task load Hard task load A1 call + activation

A3 call

A3 activation

A1 call + activation

A3 call A3 activation

3 2 5 6 4 5

5 calls & 8 activations 10 calls & 11 activations

emergency ride

ordered transport ride

Ambulance dispatcher’s task

Training Task & interface knowledge

Places on the map

Time distances between places

Trial condition

Condition Easy Hard

Duration 2 x 15 min 2 x 15 min

Measures

HR(V) and respiration frequency Eye movements NASA-TLX

Procedure & experimental design

N = 15

Remote testing lab

Operator’s workstation

Results: NASA - Task Load Index

F(1, 14)=7.19, p<0.05

Easy Hard

NA

SA

-TLX

[raw

sco

re]

HR(V) methodology

Time window (i.e. HR(V) mean values within 30 seconds)

“Spectral profiles” (indicators of spectral power as a function of time)

Har

te ra

te v

aria

bilit

y

Time line

Shifted forward each second

HR(V) methodology [cont’d] “Event analysis”

(effect of task events on mental effort)

Ride scheduling (40 sec)

No ride scheduling (40 sec)

No ride activation (40 sec)

Ride activation (40 sec)

Call Activation

emergency ride ordered transport ride

No scheduling work

F(1, 10)=31.47, p<0.001

During ride scheduling

Results: HRV around event [ordered transports] H

RV

[res

pira

tion

frequ

ency

ban

d]

HR(V) methodology [cont’d] “Event analysis”

(effect of task events on mental effort)





Call Activation


Results: HRV around event [emergency rides]

p=0.06

F(1, 12)=10.13, p<0.01

No activation work

During ride activation

Easy Hard

HR

V [r

espi

ratio

n fre

quen

cy b

and]

Spatial distribution of eye fixations [NNI]

NNI methodology

Time window (i.e. NNI by using fixations recorded in 1 minute)

Shifted forward each second

“Time series” (indicators of scanning pattern as a function of time)

Nea

rest

Nei

ghbo

r Ind

ex

Time line

NNI methodology [cont’d] “Event analysis”

(effect of task events on mental workload)





Call Activation


Hypothesis

During emergency rides activation

and during ordered rides scheduling

visual scanning pattern should be

more spread (i.e. more random)

respect to the segments where these

activities were not required.

Conclusions

HRV -in respiration frequency band-

showed to be sensitive to momentary

increases and decreases in invested effort

during different task events.

NNI should indicate a dispersed visual

exploration strategy in the short task

phases where addit ional cognit ive

resources may be requested.

Discussion

Most human operations are characterised by

unexpected situations.

Critical events could lead to instantaneous

peaks in invested effort.

“Event-based” methodologies might detect

these peaks and provide psychophysiological

indexes to use as trigger of adaptive supports.

Thank you for your attention…

[email protected]

HFES – Europe Chapter Annual Meeting October 14-16, 2009. Linköping: Sweden.

Camilli HFES-EC 2009

Engineering

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