Design and Procedure

A within-subjects design was used in which each participant was presented with a series of choice options (either five practice followed by twenty main choice trials in Experiments 1 and 2, or four sets of six choice trials in the remaining experiments using the CCT. See individual experimental sections for details). Participants were briefed on the nature of the study, invited to sign a consent form prior to participation, and reminded of their right to withdraw. Participants were given typed instructions which were also read aloud by the experimenter. The general and practice instructions were read and participants received the practice task. Following the practice, the experimenter read the main task instructions and participants then received the main task. The instructions, the brief and debrief used simple vocabulary and were clear and concise to facilitate participants' comprehension of the task. Participants were asked if they had any questions before the start of both the practice and main tasks. Providing the experimenter was satisfied that participants understood the task

110

following the practice, participants received the main task. Participants had no previous experience of the novel CCT, but were familiar with using computers.

The delayed amount remained constant (10 pence) throughout each CCT testing session. The immediate reward amount always started as half the delayed amount (5 pence) and was adjusted depending on the participant’s previous choice. This initial adjusting procedure was designed with the aim of converging on a point of indifference that a participant could reach and sustain within a fixed number of choices. For this reason, the adjustments were generated using a procedure similar to the DAA (Du, Green & Myerson, 2002). However, as the current research presented participants with smaller monetary reward amounts and more than six choice trials per delay (in Experiments 1 and 2), the adjustment procedure was modified to suit the present project. This involved halving the immediate (SS) amount (this value was rounded by the computer program to whole pennies) and either adding or subtracting it to the original immediate value to generate the next immediate amount (Table 2.1).

111

Table 2.1 Adjustments of SS values when SS is previously chosen and when LL is previously chosen. SS value presented Choose SS (- half SS) Next SS value = Choose LL (+ half SS) Next SS value = 10p SS 5p (- 5) 10p (+ 5) 9p SS 4p (- 4.5 (5)) 10p (+ 4.5 (5)) 8p SS 4p (- 4) 10p (+ 4) 7p SS 3p (- 3.5 (4)) 10p (+ 3.5 (4)) 6p SS 3p (- 3) 9p (+ 3) 5p SS 2p (- 2.5 (3)) 8p (+ 2.5 (3)) 4p SS 2p (- 2) 6p (+ 2) 3p SS 1p (- 1.5 (2)) 5p (+ 1.5 (2)) 2p SS 1p (- 1) 3p (+ 1) 1p SS 0p (- 0.5 (1)) 2p (+ 0.5 (1)) 0p SS 0p (- 0) *0p (+ 0)

Note: *Exception to the rule would be when a participant reaches 0p SS versus 10p LL. If 10p LL is chosen in this instance, the next SS value would be

increased to 1p SS rather than continuing at 0p SS for the remaining trials to permit participants to reach higher indifference points if desired.

Specifically, if the participant chose 5p (pence) immediately in the initial 5p (more immediate) versus 10p (delayed) option, the next option generated would be 2p (immediately) versus 10p (after a delay); if the participant chose to have 10p after a delay their next choice would be 8p (immediately) versus 10p (after a delay). Figure 2.2 illustrates this and several other examples of different

112

Figure 2.2 Flow diagram of possible pathways proposed for adjusted choice options presented and chosen in the CCT.

Solanto et al. (2001) and Hoerger and Mace (2006) presented participants with practice trials to familiarise participants with the choice task. Specifically, Hoerger and Mace used a series of unrewarded forced choice trials where each participant experienced the same specific aspects of the task. Therefore, in accordance with these studies, participants in the current research project were presented with a series of practice trials to reduce anxiety and facilitate understanding.

In Experiments 1 and 2 practice tasks required participants to press a button on a joystick to make the gun move left or right according to a random sequence determined by the computer program. No choice was required and no monetary

113

rewards were received during the practice trials. For the remaining experiments however, practice trials were identical to choice trials in the main task, but involved smaller delays (see individual experimental chapters for more details).

For the main choice tasks participants were presented with two spaceships worth different monetary amounts. Participants moved the joystick left or right in the direction of the spaceship they wanted to choose. The gun would then move across the bottom of the screen towards the chosen spaceship to a point vertically in line with it and fire a shot to destroy the spaceship. The reward value associated with the spaceship would be added to the total score and the next choice trial would commence. This would be repeated until all the trials (specified in each experimental chapter of the current thesis) had been completed.

Each option presented, each choice made and the associated response times (in milliseconds) were recorded automatically by the computer. Response Times (RT) were recorded from the presentation of the choice to the point at which the participant moved the joystick left or right. The experimenter debriefed each participant after completion of the CCT and the one-penny coins were changed into larger denominations. For all experiments (except Experiments 3 and 4 involving university students) each participant was then escorted back to his living area or classroom and relevant staff were given the participant’s monetary reward by the experimenter for the total amount scored. The member of staff signed to confirm receipt of the money and added to the participant's money box. The student participants in Experiments 3 and 4 were debriefed at the end of the experiment, the experimenter changed the one-

114

penny coins into larger denominations and given their monetary reward for the total amount they had scored after the testing session.

Experiment 1

Suitability and Effectiveness of the CCT (Part I)