Static versus dynamic judgments of spatial extent.

Research exploring how scanning affects judgments of spatial extent has produced conflicting results. We conducted four experiments on line bisection judgments measuring ocular and pointing behavior, with line length, position, speed, acceleration, and direction of scanning manipulated. Ocular and pointing judgments produced distinct patterns. For static judgments (i.e., no scanning), the eyes were sensitive to position and line length with pointing much less sensitive to these factors. For dynamic judgments (i.e., scanning the line), bisection biases were influenced by the speed of scanning but not acceleration, while both ocular and pointing results varied with scan direction. We suggest that static and dynamic probes of spatial judgments are different. Furthermore, the substantial differences seen between static and dynamic bisection suggest the two invoke different neural processes for computing spatial extent for ocular and pointing judgments.

Functional MRI of dynamic judgments of spatial extent.

Judgments of spatial relationships are often made when the object or observer is moving. Behaviourally, there is evidence that these 'dynamic' judgments of spatial extent differ from static judgments. For example, in one of the simplest probes of spatial extent--the line bisection task--the typically observed leftward bisection bias of about 1% of line length is increased considerably after left-to-right scanning. Here we used fMRI to examine whether or not different brain regions would be involved in static and dynamic judgments of spatial extent. Dynamic (i.e., scan the line prior to bisecting) relative to static ocular bisections (i.e., line bisection by fixation) produced activations in the cuneus and precuneus bilaterally, with reduced activation relative to static judgments observed in the supramarginal gyrus bilaterally. Dynamic bisections relative to a control condition (i.e., scan a line and then saccade to a transection mark) produced activations in the precuneus/superior parietal lobe bilaterally and left cerebellum. Only marginal evidence was found for different activations due to the initial scan direction of the line. These results highlight the fact that dynamic judgments of spatial extent use distinct brain regions from those employed to make static judgments, and the same mechanism is employed independent of scan direction. It may be the case that velocity processing and time estimates are integrated primarily in the cuneus and precuneus to produce estimates of spatial extent under dynamic scanning conditions.

Examining the influence of 'noise' on judgements of spatial extent.

The line bisection task--commonly used as a clinical measure of unilateral neglect--requires participants to place a mark on a horizontal line to indicate where they think centre is. In general, results suggest that the allocation of attention mediates bisection. In addition, previous research shows that participants rarely explore the endpoints of lines, suggesting that peripheral visual information informs bisection. Here, we examined bisection performance under conditions in which differing levels of 'noise' were introduced to the line to examine the hypothesis that the fidelity and symmetry of peripheral information would inform performance. Contrary to our expectations, results showed that symmetrically introducing noise to the line biased bisection further leftward compared to a 'no-noise' condition. Furthermore, asymmetrical noise increased leftward bisection errors primarily when lines were presented in left space or when the greater amount of noise was on the left half of the line. These results indicate that the fidelity of peripheral visual information mediates bisection behaviour that is already biased leftwards probably due to right hemisphere attentional mechanisms.

Integrating Followership Into Leadership Programs.

Followership is more than just a topic to be tacked on to the body of a leadership program; it fundamentally alters the way students engage with leadership theory and practice. In this chapter, the authors draw on 15 years of experience supporting, modifying, and delivering followership training within leadership programs to provide the unique planning and design elements required to include followership into leadership programs, along with samples of course design and practical classroom activities.

Finding centre: ocular and fMRI investigations of bisection and landmark task performance.

The line bisection task is used as a bedside test of spatial neglect patients who typically bisect lines to the right of true centre. To disambiguate the contribution of perceptual from motor biases in bisection, previous research has used the landmark task in which participants determine whether a transection mark is left or right of centre. One recent study using stimuli that reliably leads to leftward perceptual biases in healthy individuals, found that ocular judgements of centre were biased to the right of centre, whereas manual bisections were biased leftwards. Here we used behavioural measures and functional MRI in healthy individuals to investigate ocular and perceptual judgements of centre. Ocular judgements were made by having participants fixate the centre of a horizontal bar that was dark at one end and light at the other (i.e., a 'greyscale' stimulus), whereas perceptual responses were made by having participants indicate whether a transection mark on the greyscales stimuli was to the left or right of centre. Behavioural data indicated a leftward bias in the first, second and longest fixations for bisection. Moreover, greyscale orientation (i.e., dark extremity to the right or to the left), and stimulus position modulated fixations. In contrast, for the landmark task, initial fixations were attracted towards the transection mark, whereas subsequent fixations were closer to veridical centre. Imaging data showed a large bilateral network, including superior parietal and lingual cortex, that was active for bisection. The landmark task activated a predominantly right hemisphere network including superior and inferior parietal cortices. Taken together these results indicate that very different strategies and underlying neural networks are invoked by the bisection and landmark tasks.

Multimodal temporal perception deficits in a patient with left spatial neglect.

We examined multisecond time estimation (up to 60 s) for visual and auditory events in a patient with left spatial neglect (RR), who grossly underestimated all durations in all tasks. In contrast, healthy controls and a patient with left hemisphere damage (HW) demonstrated accurate estimates of the same durations. These findings add to a growing body of literature suggesting that neglect cannot be understood simply in terms of a bias in orienting attention to one side of space. In addition, these data suggest that the right hemisphere parietal cortex may be important for the perception of time across multiple modalities.