Moving to Directly Cued Locations Abolishes Spatial Interference During Bimanual Actions

Interference is frequently observed during bimanual movements if the two hands perform nonsymmetric actions. We examined the source of bimanual interference in two experiments in which we compared conditions involving symmetric movements with conditions in which the movements were of different amplitudes or different directions. The target movements were cued either symbolically by letters or directly by the onset of the target locations. With symbolic cues, reaction times were longer when the movements of the two hands were not symmetric. With direct cues, reaction times were the same for symmetric and nonsymmetric movements. These results indicate that directly cued actions can be programmed in parallel for the two hands. Our results challenge the hypothesis that the cost to initiate nonsymmetric movements is due to spatial interference in a motor-programming stage. Rather, the cost appears to be caused by stimulus identification, response-selection processes connected to the processing of symbolic cues, or both.     

The big shill

Shills are people who endorse products and companies for pay, while pretending that their endorsements are ingenuous. Here we argue that there is something objectionable about shilling that is not reducible to its bad consequences, the lack of epistemic conscientiousness it often relies upon, or to the shill's insincerity. Indeed, we take it as a premise of our inquiry that shilling can sometimes be sincere, and that its wrongfulness is not mitigated by the shill's sincerity, in cases where the shill is sincere. Our proposal is that the shill's defining characteristic is their knowingly engaging in a kind of speech that obscures a certain aspect of its social status—most commonly, by pretending to speak on their own personal behalf, while in fact speaking as an employee—and that this sort of behaviour is objectionable irrespective of any other features of the shill's conduct. This sort of obfuscation undermines a socially beneficial communicative custom, in which we conscientiously mark the distinction between personal speech and speech-for-hire.     

Development of a new spatial test

The development of a new colored spatial test is described. Some psychometric characteristics of this new test are presented from a correlational study, and some suggestions about its incorporation into research are offered.     

Shifty characters

In “Demonstratives”, David Kaplan introduced a simple and remarkably robust semantics for indexicals. Unfortunately, Kaplan’s semantics is open to a number of apparent counterexamples, many of which involve recording devices. The classic case is the sentence “I am not here now” as recorded and played back on an answering machine. In this essay, I argue that the best way to accommodate these data is to conceive of recording technologies as introducing special, non-basic sorts of contexts, accompanied by non-basic conventions governing the use of indexicals in those contexts. The idea is that recording devices allow us to use indexicals in new and innovative ways to coordinate on objects. And, given sufficient regularity in the use of indexicals on such devices, linguistic conventions will, over time, come to reflect this innovation. I consider several alternatives to this ‘character-shifting’ theory, but none is able to account for the data as well as the present proposal. Many face additional theoretical difficulties as well. I conclude by explaining how the character-shifting theory not only retains many of the virtues of Kaplan’s original semantics, but also coheres with a plausible view on the nature of semantic theorizing more generally.     

The role of input and output modality pairings in dual-task performance: evidence for content-dependent central interference

Recent debate regarding dual-task performance has focused on whether costs result from limitations in central capacity, and whether central operations can be performed in parallel. While these questions are controversial, the dominant models of dual-task performance share the assumption that central operations are generic--that is, their interactions are independent of stimulus and response modalities. To examine these issues, we conducted a series of dual-task experiments with different input and output modality pairings. One condition combined a visual-manual task with an auditory-vocal task, and the other condition reversed the input-output pairings, combining a visual-vocal task with an auditory-manual task. Input/output modality pairings proved to be a key factor; throughout practice, dual-task costs were generally more than twice as large with visual-vocal/auditory-manual tasks than with the opposite arrangement of modalities (Experiments 1 and 2). These differences could be explained neither by competition for peripheral resources nor by differences in single-task response times (Experiment 3). Moreover, the persistent dual-task costs did not appear to stem from a central bottleneck. Contrary to the dominant models of dual-task performance, we propose that central interference between tasks depends not just on the duration of central operations, nor just strategic adaptation, but also on the content of those operations. Implications for structural and strategic accounts of dual-task interference are discussed.     

Simultaneous dual-task performance reveals parallel response selection after practice

E. H. Schumacher, T. L. Seymour, J. M. Glass, D. E. Kieras, and D. E. Meyer (2001) reported that dual-task costs are minimal when participants are practiced and give the 2 tasks equal emphasis. The present research examined whether such findings are compatible with the operation of an efficient response selection bottleneck. Participants trained until they were able to perform both tasks simultaneously without interference. Novel stimulus pairs produced no reaction time costs, arguing against the development of compound stimulus-response associations (Experiment 1). Manipulating the relative onsets (Experiments 2 and 4) and durations (Experiments 3 and 4) of response selection processes did not lead to dual-task costs. The results indicate that the 2 tasks did not share a bottleneck after practice.