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R kennedy hfes 2012 visual aids
1. The Influence of Visual Aids on
Detecting Early and Late Decelerations
in Maternal Fetal Heart Rate Patterns
Rebecca A. Kennedy, Brittany L. Anderson-Montoya,
Mark W. Scerbo, Erik Prytz, Lee A. Belfore, II
Old Dominion University
Alfred Z. Abuhamad, Stephen S. Davis, Suneet P. Chauhan
Eastern Virginia Medical School
October 23, 2012
HFES 56th Annual Meeting
2. Introduction
Maternal-fetal heart rate (MFHR)
Presented on either a computer screen or a paper strip
Clinicians assess for different critical patterns
NICHD proposed a three-tiered system (Category I, Category II,
Category III) (Macones et al., 2008)
3. Introduction
Clinicians must identify decelerations (decels) in the
FHR and discriminate between those that are early
and late in nature
Late decels are considered abnormal
Early decels look similar, but are considered reassuring
5. Introduction
Several studies have found disagreement in the
interpretation of FHR signals
Between individuals, and within the same individual at two
different points in time (Blackwall et al., 2011; Chauhan et al., 2008; Freeman,
2002)
6. Introduction
Anderson and colleagues have assessed how well
individuals could differentiate between early and late
decels…
…under different levels of beat-to-beat FHR variability
As signal-to-noise (S/N) ratio decreased, fewer correct detections
were made (Anderson et al., 2008)
…with late decels occurring at different time frames
In the first study:
Undergraduate students had trouble differentiating types of decels,
especially at shorter onset delays (Anderson et al., 2010)
In a second study:
Trained clinicians produced the same pattern of results (Anderson et al., 2011)
7. Introduction
Results from previous studies suggest that the
inspection of FHR tracings might be improved with a
visual aid
Visual cues can help direct attention, increase
accuracy, and decrease response time (Wickens & Hollands,
2000; Chaney & Teel, 1967)
8. Present Study
Purpose: examine how well individuals can differentiate
between early and late decels using
Four different signal-to-noise ratios (absent, minimal,
moderate, marked)
Five different onset times (0, 4, 8, 12, and 16 sec)
With and without the visual aids
Hypothesis: visual aid would act as a cue and would
improve detection performance
Primarily at lower S/N ratios and shorter late decel onset times
9. Method
Participants were 21 undergraduate students (14
male; 7 female) from ODU
Ranged in age from 18 to 24 (M = 19.33)
All had normal or corrected-to-normal vision
10. Method
Static images were created using a MFHR simulator
Each image contained one contraction and either a late
decel or early decel
11. Method
Four S/N ratios for FHR were generated
Conformed to the four categories designated by the
NICHD
Absent
S/N Ratio =
10:1
Moderate
S/N Ratio = 2:1
Minimal
S/N Ratio = 5:1
Marked
S/N Ratio =
1:1
12. Method
For the visual aid condition, a semitransparent
turquoise crosshair cursor was overlaid on the image
Horizontal bar placed at mean of beat-to-beat FHR
variability
Vertical bar placed at the peak of the contraction
13. Method
Prior to the experimental session, participants viewed
examples of early and late decels
Responded verbally to 8 practice images
In the experimental session, participants twice viewed
the same 80 images
Image presented for 3 sec, after which a response screen
appeared
Session performed in two blocks – with/without visual aids
14. Results
2 (aid presence) x 2 (block order) x 4 (variability) x 5
(signal delay) mixed factorial ANOVA
Order of aid-absent and aid-present blocks was a between
subjects factor
DV was proportion of correct identifications (early or
late)
15. Results
Significant main effect of visual aid presence, F(1, 19) =
25.23, p < .05, partial ƞ2 = .570
Aid present Aid absent
.74 (.02) .66 (.02)
Mean (and standard error) proportion of correct
detections for each aid condition
16. Results
Significant Delay x Variability interaction, F(12, 228) =
13.25, p < .05, partial ƞ2 = .411
Mean proportion of correct detections for each
S/N ratio and signal onset delay
Proportion of
correct detections
17. Results
For late decels, correct responses increased as
delayed onset increased
Sidak Bonferroni test indicated that all means were significantly
different except between 0- and 12- sec, 0- and 16-sec, and 8- and
12-sec delays
Mean SE
0 sec 0.83 0.03
4 sec 0.40 0.04
8 sec 0.69 0.03
12 sec 0.74 0.02
16 sec 0.84 0.02
Mean proportions of correct responses for each signal onset delay
Note: A delay of 0 indicates an early deceleration
18. Results
As S/N ratio decreased (i.e., variability increased),
correct response rate decreased
Sidak Bonferroni test indicated that all means differed significantly,
except for between the absent and minimal categories
Mean SE
Absent 0.81 0.02
Minimal 0.80 0.02
Moderate 0.69 0.02
Marked 0.50 0.02
Mean proportions of correct responses for each level of variability
19. Discussion
Hypothesis: visual aids would improve detection
performance especially for lower S/N ratios and shorter
onset times
Partially supported
Presence of visual aids was associated with higher overall levels of
correct responses
Delay x Variability interaction revealed that the benefit of the visual
aid was seen primarily in the minimal variability category
However, under lower S/N ratios (moderate and marked
variability), the aid did not make a statistically significant
difference
Presence of decels may be masked to such a degree that aids do
not help
20. Conclusion
The results provide initial evidence that a visual aid
was useful
However, the visual aid is not a complete solution
Decels occurring at moderate and marked levels of FHR
variability, especially with short onsets, are still
problematic
A next step is to evaluate the potential benefit of the
visual aid with clinical providers manipulating the
visual aid in real time
