On the interpretation of likelihood ratios in forensic science evidence: Presentation formats and the weak evidence effect.

Likelihood ratios are increasingly being adopted to convey expert evaluative opinions to courts. In the absence of appropriate databases, many of these likelihood ratios will include verbal rather than numerical estimates of the support offered by the analysis. However evidence suggests that verbal formulations of uncertainty are a less effective form of communication than equivalent numerical formulations. Moreover, when evidence strength is low a misinterpretation of the valence of the evidence - a "weak evidence effect" - has been found. We report the results of an experiment involving N=404 (student and online) participants who read a brief summary of a burglary trial containing expert testimony. The expert evidence was varied across conditions in terms of evidence strength (low or high) and presentation method (numerical, verbal, table or visual scale). Results suggest that of these presentation methods, numerical expressions produce belief-change and implicit likelihood ratios which were most commensurate with those intended by the expert and most resistant to the weak evidence effect. These findings raise questions about the extent to which low strength verbal evaluative opinions can be effectively communicated to decision makers at trial.

Perceptual and physiological responses to the visual complexity of fractal patterns.

Fractals have experienced considerable success in quantifying the complex structure exhibited by many natural patterns and have captured the imagination of scientists and artists alike. With ever widening appeal, they have been referred to both as "fingerprints of nature" and "the new aesthetics." Our research has shown that the drip patterns of the American abstract painter Jackson Pollock are fractal. In this paper, we consider the implications of this discovery. We first present an overview of our research from the past five years to establish a context for our current investigations of human response to fractals. We discuss results showing that fractal images generated by mathematical, natural and human processes possess a shared aesthetic quality based on visual complexity. In particular, participants in visual perception tests display a preference for fractals with mid-range fractal dimensions. We also present recent preliminary work based on skin conductance measurements that indicate that these mid-range fractals also affect the observer's physiological condition and discuss future directions based on these results.

The relationship between the structural mere exposure effect and the implicit learning process.

Three experiments are reported that investigate the relationship between the structural mere exposure effect (SMEE) and implicit learning in an artificial grammar task. Subjects were presented with stimuli generated from a finite-state grammar and were asked to memorize them. In a subsequent test phase subjects were required first to rate how much they liked novel items, and second whether or not they thought items conformed to the rules of the grammar. A small but consistent effect of grammaticality was found on subjects' liking ratings (a "structural mere exposure effect") in all three experiments, but only when encoding and testing conditions were consistent. A change in the surface representation of stimuli between encoding and test (Experiment 1), memorizing fragments of items and being tested on whole items (Experiment 2), and a mismatch of processing operations between encoding and test (Experiment 3) all removed the SMEE. In contrast, the effect of grammaticality on rule judgements remained intact in the face of all three manipulations. It is suggested that rule judgements reflect attempts to explicitly recall information about training items, whereas the SMEE can be explained in terms of an attribution of processing fluency.