Seizure detection in subdural recordings using nonlinear decision functions

This dissertation proposed a new approach to seizure detection in intracranial EEG recordings using nonlinear decision functions. It implemented well-established features that were designed to deal with complex signals such as brain recordings, and proposed a 2-D domain of analysis. Since the features considered assume both the time and frequency domains, the analysis was carried out both temporally and as a function of different frequency ranges in order to ascertain those measures that were most suitable for seizure detection. In retrospect, this study established a generalized approach to seizure detection that works across several features and across patients. ^ Clinical experiments involved 8 patients with intractable seizures that were evaluated for potential surgical interventions. A total of 35 iEEG data files collected were used in a training phase to ascertain the reliability of the formulated features. The remaining 69 iEEG data files were then used in the testing phase. ^ The testing phase revealed that the correlation sum is the feature that performed best across all patients with a sensitivity of 92% and an accuracy of 99%. The second best feature was the gamma power with a sensitivity of 92% and an accuracy of 96%. In the frequency domain, all of the 5 other spectral bands considered, revealed mixed results in terms of low sensitivity in some frequency bands and low accuracy in other frequency bands, which is expected given that the dominant frequencies in iEEG are those of the gamma band. In the time domain, other features which included mobility, complexity, and activity, all performed very well with an average a sensitivity of 80.3% and an accuracy of 95%. ^ The computational requirement needed for these nonlinear decision functions to be generated in the training phase was extremely long. It was determined that when the duration dimension was rescaled, the results improved and the convergence rates of the nonlinear decision functions were reduced dramatically by more than a 100 fold. Through this rescaling, the sensitivity of the correlation sum improved to 100% and the sensitivity of the gamma power to 97%, which meant that there were even less false negatives and false positives detected. ^

Perceptions of alibi evidence as a function of the strength of incriminating *evidence

The current study investigated the exculpatory value of alibi evidence when presented together with various types of incriminating evidence. Previous research has reported that alibi evidence could weaken the effects of DNA evidence and eyewitness identification. The present study assessed the effectiveness of alibi evidence in counteracting defendant's confession (experiment 1) and eyewitness evidence (experiment 2). In experiment 1, three levels of alibi evidence (none, weak, strong) were combined with three levels of confession evidence (voluntary, elicited under low pressure, elicited under high pressure). Results indicated significant main effects of confession and alibi and an alibi by confession interaction. Of participants exposed to high-pressure confession, those in the strong alibi condition rendered lower guilt estimates than those in the no alibi condition. In experiment 2, three levels of alibi were combined with two levels of eyewitness evidence (bad view, good view). A main effect of alibi was obtained, but no interaction between alibi and eyewitness evidence. ^ An explanation of this pattern is based in part on the Story Model (Pennington & Hastie, 1992) and a novel “culpability threshold” model of juror decision-making. The Story Model suggests that jurors generate verdict stories (interpretations of events consistent with a guilty or not guilty verdict) based on trial evidence. If the evidence in favor of guilt exceeds jurors' threshold for perceiving culpability, jurors will fail to properly consider exonerating evidence. However, when the strength of incriminating evidence does not exceed the jurors' threshold, they are likely to give appropriate consideration to exculpatory evidence in their decisions. ^ Presentation of a reliable confession in Experiment 1 exceeded jurors' culpability threshold and rendered alibi largely irrelevant. In contrast, presentation of a high-pressure confession failed to exceed jurors' culpability threshold, so jurors turned to alibi evidence in their decisions. Similarly, in the second experiment, eyewitness evidence (in general) was not strong enough to surpass the culpability threshold, and thus jurors incorporated alibi evidence in their decisions. A third study is planned to further test this “culpability threshold” model, further explore various types of alibi evidence, and clarify when exculpatory evidence will sufficiently weaken the prosecution's “story.” ^