This study will employ a randomized mixed between-within experimental stress-testing protocol design. Physiological responses (blood pressure and pulse) will be recorded throughout a baseline, gratitude induction, standard stress-task and recovery period. Participants will be randomly allocated to the experimental (grateful induction) or control condition (neutral induction). Gratitude will be induced by completing a gratitude letter. Demographics will be measured. Psychosocial and health variables will be measured psychometrically at baseline to assess pre-existing levels and after both manipulations (allocated induction and stress task) to monitor expected change over time between conditions. Stress task is an adapted version of the Trier Stress Testing protocol.

This study will employ an experimental within-subjects design, in which all participants are exposed to the same task and measures. The study will take place in Cubicle 1 of the Psychology Department, 2nd floor John Hume Building. On entry into the lab, participants will first be required to read the study information sheet and provide informed consent before the formal testing session begins. This standard protocol will comprise of the collection of demographic information, the administration of questionnaires (See supporting documentation) and the monitoring of physiological responses. The monitoring phase involves the following periods, a 20 minute acclimatisation, 10 minute baseline, 8 minute intervention, a 12-stress task and a 10 minute recovery period. During baseline general socio-demographic and lifestyle information will be collected through standard questionnaires (e.g. age, gender, height smoking status, health status and family history pertaining to the cardiovascular system; see supporting documentation). If predictive of blood pressure in the current study all potential confounds will be controlled for statistically in relevant analyses to isolate the contribution of the predictor variables, in this case state and trait gratitude, to the cardiovascular changes. Physiological responses -systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR)- will be measured noninvasively using a GE Dinamap Pro 400 and will be recorded throughout with a standard blood pressure cuff placed over the brachial artery on the participant's non-dominant arm. During the baseline phase psychological variables will be measured psychometrically.

Following this baseline phase, participants will randomly be allocated to either the control or experimental condition. The experimental condition will involve writing a letter thanking someone the participant had not thanked before. The control group will complete a writing exercise wherein they describe the laboratory room. They will have 8 minutes to complete this.

Following this intervention phase, participants will then complete an adapted form of the widely used Trier Social Stress Test, which involves participants subtracting numbers out loud and giving a short speech wherein they describe three of their best and worst characteristics . After the stress task, in the recovery phase participants will answer a series of questions pertaining to how they found the stress task. They will then sit for 8 minutes while recovery measures are taken.

Following this, all participants will be fully debriefed (supporting documentation) and thanked for their participation.

Inclusion Criteria:

• 18 years and older
• Able to consent

Exclusion Criteria:

• Participants with a diagnosis of cardiovascular disease, hypertension, oran immune disorder
• Participants who are pregnant.
• Participants taking medication influencing cardiovascular measures.
• Participants who consumed alcohol 12 hours before study.
• Participants who exercised 12 hours before study.
• Participants who consumed nicotine 2 hours before study.
• Participants who consumed caffeine 2 hours before study.
• Participants who ate 1 hour before study.