Symposium Presentation 3 – expectancy, water consumption and cognition

Expectancy and the water consumption effect

Caroline J Edmonds, Rosanna Crombie, Haiko Ballieux, Mark R Gardner and Lynne Dawkins


Objectives:  The positive effect of water consumption on letter cancellation task performance has been well established. The present study considered whether these effects are due to water consumption, or expectations about the effects of water consumption.

Design: Participants were told that the study would examine the effect of repeated testing over time. They were assigned to one of four conditions: Water, Expectancy; Water, No Expectancy; No Water, Expectancy; No Water, No Expectancy (water n = 24, after exclusions). Performance was assessed at baseline and Test.

Methods: Forty seven participants (aged 18 to 57 years) were recruited. Participants in the Expectancy groups were given the expectation that water positively affects cognition. All participants completed Thirst and Mood scales, Letter Cancellation, Forwards and Backwards Digit Span, and Simple Reaction Time tasks.

Results: Three participants were removed from analyses because they were in the Water group but did not drink. Difference scores were calculated by subtracting performance scores at baseline from those at Test. Those who drank water were significantly less thirsty, compared to those who did not have a drink. They also had a significantly greater improvement in Letter Cancellation performance, compared to those in the No Water condition. This water consumption effect did not interact with expectancy in the case of Letter Cancellation.

Conclusions: The effect of water consumption on Letter Cancellation performance appears to result from the physiological effects of water consumption, and not from expectancies about the effect of consumption.

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