Sex differences in human sign/goal tracking behaviour as measured by Pavlovian Conditional Approach scores in a virtual cue-reward environment

Arts, Peter (2023). Sex differences in human sign/goal tracking behaviour as measured by Pavlovian Conditional Approach scores in a virtual cue-reward environment. Student research project for the Open University module SXH390 Health Sciences Project Module

This dissertation was produced by a student studying the Open University module SXH390 Health Sciences Project Module. The research showcased here achieved a grade in either the Pass 1 band (equivalent to a 1st) or the Pass 2 band (equivalent to a 2.i).
Please note that this student dissertation is made available in the format that it was submitted for examination, thus the author has not been able to correct errors and/or departures from academic standards in areas such as referencing.
Copyright resides with the author.




Through Pavlovian classical conditioning, cues repeatedly associated with rewards can become conditioned stimuli, exerting strong influences on behaviour. Drug-linked cues can become motivational magnets soliciting approach and increasing addiction vulnerability. Animal studies have demonstrated individual differences in cue-reactivity: sign-trackers preferentially approach the cue vs goal-trackers the rewards. Importantly, these differences are associated with different risks and course of addiction. However, studies on human sign-tracking/goal-tracking phenotypes are limited, and sex differences remain unexplored. This study aimed to fill this gap.


Participants were asked to collect virtual coin rewards in a virtual room. A coloured light presentation preceding reward delivery and co-located lever functioned as conditioned stimulus; a control light and lever were also included. Data from 316 participants (144 females/172 males) was collected for directed click counts/latencies/densities, allowing calculation of Pavlovian conditioned approach scores and testing these for female/male differences. Survey results were collected on impulsivity and task understanding.


Median male Pavlovian conditioned approach scores were found to be significantly (p<0.001,α=5%,bidirectional) higher, i.e. more towards the sign-tracking phenotype, than those for females (0.444 vs 0.000). Analysis of sub-metrics (including response bias) and scores for early/late trials yielded equally significant male/female differences. However, no significant association was found between approach behaviour and impulsivity. Furthermore, scores using the control stimulus showed equally significant male/female differences as for the conditioned stimulus.


In this study, approach score results suggested males are more sign-tracking than females. This finding would be novel in humans, and possibly unexpected given animal results. If confirmed, such sex differences could have important implications for addiction treatment and prevention. However, absence of any impulsivity association, and similarity of control and conditioned stimulus score results, challenged these findings. Results may instead reflect outright preferential lever interaction or point to study limitations (e.g. metric/reward choice), thus requiring further study.

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