Repetition of Computer Security Warnings Results in Differential Repetition Suppression Effects as Revealed With Functional MRI.

Computer users are often the last line of defense in computer security. However, with repeated exposures to system messages and computer security warnings, neural and behavioral responses show evidence of habituation. Habituation has been demonstrated at a neural level as repetition suppression where responses are attenuated with subsequent repetitions. In the brain, repetition suppression to visual stimuli has been demonstrated in multiple cortical areas, including the occipital lobe and medial temporal lobe. Prior research into the repetition suppression effect has generally focused on a single repetition and has not examined the pattern of signal suppression with repeated exposures. We used complex, everyday stimuli, in the form of images of computer programs or security warning messages, to examine the repetition suppression effect across repeated exposures. The use of computer warnings as stimuli also allowed us to examine the activation of learned fearful stimuli. We observed widespread linear decreases in activation with repeated exposures, suggesting that repetition suppression continues after the first repetition. Further, we found greater activation for warning messages compared to neutral images in the anterior insula, pre-supplemental motor area, and inferior frontal gyrus, suggesting differential processing of security warning messages. However, the repetition suppression effect was similar in these regions for both warning messages and neutral images. Additionally, we observed an increase of activation in the default mode network with repeated exposures, suggestive of increased mind wandering with continuing habituation.

Effects of an exercise program to increase hip abductor muscle strength and improve lateral stability following stroke: a single subject design.

BACKGROUND AND PURPOSE: Persons with lower extremity weakness following stroke often demonstrate difficulty with weight transfer and paretic lower extremity loading. These deficits, in turn, can lead to problems with lateral stability, or the ability to control movement of the center of mass in the frontal plane. The primary aim of this study was to examine the efficacy of an individualized home exercise program in improving hip abductor muscle strength and lateral stability in a subject with chronic stroke. METHODS: An A-B-A treatment-withdrawal single-subject design was used. The subject was a 70-year-old male who had experienced a left hemispheric stroke 36 months prior to initiation of the study. Bilateral hip abductor muscle strength, single limb stance (SLS), timed 360 degrees turn, Step Test, and 10-m walk at self-selected and fast speeds were recorded at regular intervals during the baseline (A-I), treatment (B), and treatment-withdrawal (A-2) phases. The home exercise program in the B phase consisted of lower extremity weight bearing and weight transfer activities and exercise on a lateral training device 3 to 5 times a week for 6 weeks. The Berg Balance Scale (BBS) and Stroke Impact Scale (SIS) were administered at the completion of each phase and at 6-week follow-up. Data were analyzed using visual analysis and the split-middle method of trend estimation. RESULTS: Mean levels of all measures improved from A-1 to B phases, with significant increases in trend for hip abductor muscle strength and SLS bilaterally. Most improvements were maintained during the treatment-withdrawal (A-2) phase and at follow-up. CONCLUSION: A home exercise program that includes exercise on a lateral training device shows promise for producing increases in hip abductor muscle strength and accompanying improvements in some measures of physical performance and disability in persons with chronic stroke.