Fred Shaffer, Ph'D', Logan Banks, Adam Lipps, Ian Lynam, Susan Jacobsmeyer, and Kathryn Rumora

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The Effects of Instructions, Sitting Position,
and Task on Baseline Measurements

• Fred Shaffer, Ph.D., Logan Banks, Adam Lipps, Ian
  Lynam, Susan Jacobsmeyer, and Kathryn Rumora 
• Truman State University

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Important Questions

• Can the phrasing of preparatory baseline
  instructions influence psychophysiological
  measurements?
• Can sitting position affect baseline
  measurements?

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Purpose

• The present factorial experiment studied the
  effect of preparatory instructions (low-detail
  or high-detail) and sitting position (upright or
  reclining) on psychophysiological measurements

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Purpose

• These measurements included
• frontal sEMG
• blood volume pulse
• heart rate
• respiration rate
• skin conductance level
• skin temperature

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Participants

• Sixty-three undergraduate students (8 men and 55
  women) volunteered for academic credit
• They ranged from 18 to 23 years of age

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Apparatus

• A J J I-330 Physiological Monitoring System
  measured musculoskeletal (frontal sEMG) and
  autonomic variables (blood volume pulse, heart
  rate, respiration rate, skin conductance level,
  and skin temperature)

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Apparatus

• We measured frontal sEMG using an M-501 module
  (25-1000 Hz bandpass) and 10-mm
  silver/silver-chloride surface electrodes placed
  over the frontales muscle

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Apparatus
Frontales sEMG
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Apparatus

• We detected blood volume pulse and heart rate
  using a P-401 module and PPG (photoplethysmograph)
  sensor placed over the index finger of the
  nondominant hand

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Apparatus
PPG sensor
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Apparatus

• We measured respiration rate using a R-301 module
  and a K-S Industries breathing harness, which
  consists of strain gauges placed over the abdomen
  and thorax

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Respiration rate
K-S Industries Breathing Harness
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Apparatus

• We assessed skin conductance level using a T-601
  module and two SE-35 zinc electrodes placed over
  the second phalanx of the third and fourth
  fingers of the dominant hand

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Apparatus
SCL sensor
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Apparatus

• We monitored skin temperature using a T-601
  module and TS-600 thermistor (1-s time constant)
  placed over the web dorsum of the nondominant hand

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Apparatus
Web dorsum placement
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Procedure

• All subjects completed the following 3-min
  conditions
• baseline
• mental arithmetic
• buffer period
• baseline
• mental arithmetic

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Procedure

• We randomly assigned subjects to one of two
  orders of sitting position (within-subjects
  variable) upright-reclining or reclining-upright

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Procedure

• We also randomly assigned subjects to receive
  either low-detail or high-detail instructions
  (between-subjects variable)

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Procedure

• The low-detail instructions stated, Please sit
  back for the next few minutes
• The high-detail instructions stated, Please sit
  quietly with your eyes open for the next few
  minutes and try not to move

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Procedure

• After baseline and mental arithmetic conditions,
  we asked subjects to rate their degree of tension
• Please rate the level of tension you experienced
  in the last condition from 1 to 7, where 1 is the
  least tense and 7 is the most tense you can
  imagine

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Procedure

• We asked subjects during each 3-min buffer period
  to Please sit quietly with your eyes open for
  the next 3 minutes

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Results Frontal sEMG

• There was a significant interaction between task
  (rest or serial sevens) and position (sitting
  upright or reclining), F(1, 61) 8.08, p .006,
  eta2 .12

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Frontal sEMG
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Results Heart Rate

• There was a significant main effect for position
  (sitting upright or reclining), F(1, 61) 4.39,
  p .04, eta2 .07

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Heart Rate
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Results Respiration Rate

• There were main effects for task and position
• task (rest or serial sevens), F(1, 61) 6.89,
  p .011, eta2 .10
• position (sitting upright or reclining), F(1, 61)
  31.72, p .0001, eta2 .34

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Results Respiration Rate

• There was a significant task x position
  interaction, F(1, 61) 4.92, p .03, eta2
  .08
• There was also a higher-order interaction for
  task x position x instructional detail, F(1, 61)
  4.94, p .03, eta2 .08

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Respiration Rate
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Results Tension Rating

• Contrary to our expectation, instructional detail
  did not significantly affect subjective ratings
  of tension.

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Results Tension Rating

• There were main effects for task and position
• Task (rest or serial sevens), F(1, 61) 7.29,
  p .009, eta2 .11
• Position (sitting upright or reclining), F(1,
  61) 212.68, p .0001, eta2 .77

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Results Tension Rating

• There was a task x position interaction, F(1,
  61) 4.18, p .045, eta2 .06

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Tension Rating
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Discussion

• Contrary to our expectations, instructional
  detail did not independently influence any of the
  psychophysiological variables or ratings of
  subjective tension
• There was only a modest higher-order task x
  position x instructional detail interaction that
  affected respiration rate

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Discussion

• As predicted, sitting position (sitting upright
  or reclining) produced main effects on heart
  rate, respiration rate, and tension ratings
• Task (baseline or stressor) produced main effects
  on respiration rate and tension ratings
• Task and position interacted to influence
  respiration rate and tension ratings

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Discussion

• Clinicians should standardize sitting position so
  that they may compare measurements within and
  across sessions

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Future Research

• Future research should attempt to replicate this
  experiment using a sample that includes
  comparable numbers of male and female clinical
  patients

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Future Research

• We also recommend that future studies include EEG
  measurements to provide a more comprehensive
  picture of how instructional detail and sitting
  position affect psychophysiological baselines

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The Truman State University Research Team