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PAMELA SADLER AND ERIK Z. WOODY
measures of cognitive effort as well, by drawing on paradigms from cog-
nitive psychology (see Ruehle & Zamansky, 1997).
Although heart-rate increase appeared to serve well in the present
study as an index of cognitive effort, it yielded rather high within-
group variances (as indicated by the standard errors we reported),
which may limit its statistical power in other applications. One possi-
bility is that the relatively high within-group variances may reflect
multiple underlying strategies among participants. Along these lines,
King and Council (1998) advanced the idea that there may be two sub-
sets of high hypnotizable people: one that responds with low effort, in
accordance with dissociated-control theory, and another that responds
more effortfully, in accordance with the social-cognitive and dissoci-
ated-experience theories (see also Barber, 1999; McConkey, Glisky, &
Kihlstrom, 1989). This hypothesis of multiple subtypes of highs would
be an important possibility to pursue in future research, for which
nonself-report indices of cognitive effort, such as heart-rate increase,
could help serve as the basis for such a discrimination.
Finally, some previous research has examined the relation of heart
rate to hypnotizability for purposes other than indexing cognitive
effort. Harris, Porges, Carpenter, and Vincenz (1993) reported that
cardiac functioning in a nonhypnotic circumstance was somewhat
strongly related to hypnotizability. Specifically, resting heart rate
was negatively correlated with hypnotizability (
r
=
−
.47) and vagal
tone positively correlated with hypnotizability (
r
= .45). It is not surprising
that these two measures were equally predictive of hypnotizability,
because they correlate about
−
.80 (see also Ruiz-Padial, Sollers, Vila,
& Thayer, 2003). However, these findings are strikingly inconsistent
with the utter lack of relation between baseline heart rate and hypno-
tizability in the present study. One difference between the two stud-
ies is that our baseline heart-rate measure was taken after a hypnotic
induction, whereas the baseline cardiac measures in Harris et al.
were taken in a nonhypnotic context. However, a series of
five previous studies in K. Bowers’s lab at the University of Waterloo
never found any relation between resting heart rate and hypnotiz-
ability, either with or without a hypnotic induction (Hughes, 1988;
Rothmar, 1986). Thus, on balance it seems questionable whether
baseline cardiac functioning has any consistent relation to hypnotiz-
ability.
Harris et al. (1993) also reported that heart-rate increases in
response to positive and negative mood inductions (again, in a
nonhypnotic setting) were related to hypnotizability. They suggested
that the common link may be individual differences in sympathetic
nervous system arousal. Although this might possibly be an interest-
ing hypothesis for future research, such a link would not explain the
present results. In particular, in our study, imagery was selected so
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