The truth revisited: Bayesian analysis of individual differencesin the truth effect

The repetition-induced truth effect refers to a phenomenon where people rate repeated statements as more likely true than novel statements. In this paper, we document qualitative individual differences in the effect. While the overwhelming majority of participants display the usual positive truth effect, a minority are the opposite—they reliably discount the validity of repeated statements, what we refer to as negative truth effect. We examine eight truth-effect data sets where individual-level data are curated. These sets are composed of 1105 individuals performing 38,904 judgments. Through Bayes factor model comparison, we show that reliable negative truth effects occur in five of the eight data sets. The negative truth effect is informative because it seems unreasonable that the mechanisms mediating the positive truth effect are the same that lead to a discounting of repeated statements’ validity. Moreover, the presence of qualitative differences motivates a different type of analysis of individual differences based on ordinal (i.e., Which sign does the effect have?) rather than metric measures. To our knowledge, this paper reports the first such reliable qualitative differences in a cognitive task

A hierarchical Bayesian approach to distinguishing serial and parallel processing

Research in cognitive psychology often focuses on how people deal with multiple sources of information. One important aspect of this research is whether people use the information in parallel (at the same time) or in series (one at a time). Various approaches to distinguishing parallel and serial processing have been proposed, but many do not satisfactorily address the mimicking dilemma between serial and parallel classes of models. The mean interaction contrast (MIC) is one measure is designed to improve discriminability of serial-parallel model properties. The MIC has been applied in limited settings because the measure required a large number of trials and lacked a mechanism for group level inferences. We address these shortcomings by using hierarchical Bayesian analyses. The combination of the MIC with hierarchical Bayesian modeling gives a powerful method for distinguishing serial and parallel processing at both individual and group levels, even with a limited number of participants and trials

A handy project : owning, perceiving, and experiencing hands

The purpose of this thesis is to explore the mental representation of hands in the context of owning, perceiving, and experiencing hands. The theoretical knowledge of the thesis is discussed in the first chapter, considering the wider concept of body representation. The second chapter reports the data from a study exploring the relationship between the sense of ownership of hands and motor control. The kinematic features of participants’ hands' movements were recorded using a motion analysis capture system and the associated brain activity was recorded using a near-infrared-spectroscopy device. Thirty-two healthy individuals participated in the study. The data show that the embodiment of a rubber hand through touch without vision does not influence the planning and execution of grasping actions (kinematic and brain imaging data). The third chapter presents a study exploring the influence of disgust on the mental representation of hands and feet in action, or motor imagery (MI). Thirty-six healthy individuals were enrolled (different participants from the study in chapter two). The data show that disgust enhances performance on MI tasks. The fourth chapter further expands the knowledge of hands-related MI abilities by comparing hand-based and foot-based MI tasks on a more implicit and explicit level (i.e. action monitoring required to solve the task). Fifty-five healthy participants participated in the data collection (different participants from the study in chapter three). Data show how differences in the mental representation of hands and feet in action imagery are specific to the degree of monitoring required, occurring only when the task is implicit; in other words, when the degree of action monitoring decreases. In the fifth chapter, a comparison between the data obtained in MI tasks executed in laboratory-based and online-based settings is presented, as the pandemic led to the opportunity to explore this aspect. This comparison shows comparable results between settings. Finally, in the sixth chapter, a general discussion of the thesis is presented, reasoning on the limitations of the various experiments and their impact. With the current thesis, I further expand the knowledge on the mental representation of hands, also considering feet as opposite body districts to hands. More in detail, my findings highlight i) that the application of the somatic RHI does not influence motion planning and execution (i.e. maximum GA) (owning hands), ii) that disgust influences our ability to mentally rotate hands and feet (perceiving hands), iii) and that the mental representation of hands and feet in action presents differences specific to the degree of action monitoring involved in solving the task (experiencing hands). The mental representation of hands is dynamic and can be influenced differently by different factors