Basic HTML Version
was developed over a series of studies by Donovan (1989) in the course
of his doctoral dissertation. Donovan found the level of difficulty to be
critical in eliciting Stroop-related effects in the hypnosis-related trait of
absorption. Jamieson and Sheehan (2002) have noted with concern the
complete absence of successful replication of valid behavioral measures
purported to demonstrate an association between hypnotic suscept-
ibility and frontally mediated executive attentional control. This is not
to say that none may be found, but replication must be a priority if
research in this area is to advance on a sound footing. Therefore, the
basic Sheehan et al. (1988) paradigm will be adopted here rather than
exploring alternative Stroop paradigms.
This study will provide the opportunity for replication of prior
effects for hypnosis on measures of Stroop performance and strategy
use. It will further attempt to cross validate the proposed impact of
hypnosis and susceptibility on SAS control by including total incon-
gruent Stroop trial errors as an alternative measure of suppressing
attention not expressed as reaction-time data. By examining the impact
of strategy versus no-strategy and effortful-concentration versus
relaxation-instruction conditions on the above measures, we hope
to clarify the status of these potential alternative explanations of
the impact of hypnosis on Stroop performance.
M
ETHOD
Participants
This study comprised 132 participants, selected from first-year
psychology students at the University of Queensland who participated
for course credit. Participants were doubly screened for their level of
hypnotic susceptibility, using two separate assessment scales on sepa-
rate occasions. This was done to ensure the reliability of their assign-
ments to the high and low susceptibility experimental conditions.
Participants were first tested on the Harvard Group Scale of Hyp-
notic Susceptibility, Form A (Shor & Orne, 1962) and later individually
tested on the Stanford Hypnotic Susceptibility Scale, Form C (SHSS:C;
Weitzenhoffer & Hilgard, 1962). Participants were assigned to the high
susceptible condition if they obtained a score of 9 or higher on each
scale and to the low susceptible condition if they obtained a score of 3 or
lower on each scale. There were 66 high susceptibles and 66 low
susceptibles in all who participated in this study.
Apparatus and Stimuli
Stimulus presentation, sequencing, and timing were controlled by
a BBC model AMT-12RGBIB microcomputer with a color monitor.
It recorded reaction times to the nearest millisecond, together with
relevant stimulus parameters and response accuracy for each trial.
236
GRAHAM A. JAMIESON
AND
PETER W. SHEEHAN
Downloaded by [ ] at 05:16 26 March 2012