Assessment of parallel movement plans by probing spatial attention

我们的环境不断地为我们提供多重机会和行动要求。在任何给定的时刻，我们必须从所有可能的动作中选择一个，并指定相应的移动度量。有证据表明，大脑同时并行地准备多个动作，动作选择是自下而上驱动的感觉运动加工中嵌入的持续竞争的结果，这种竞争受到自上而下的决策相关信息的偏见。然而，关于动作的哪些方面实际上是并行代表的，仍在争论中。人类参与者的到达轨迹通常反映了到几个当前相关目标的直接轨迹之间的平均值；运动行为的这一方面被解释为表明执行的运动是单个运动计划平均的结果。因此，这种解释假定不同动作的所有方面都是并行表示的。然而，平均化行为有时似乎取决于战略考虑。例如，当目标距离很远，或者当动作必须执行得非常快时，轨迹平均就会被放弃；这种战略性的行为变化提高了参与者的整体表现。这些策略的使用表明，在默认情况下，运动轨迹不是平均的。取而代之的是，只计算一个详细的行动计划，当这是具有战略优势的时候，这个单一的计划可以作为一个平均值得出。因此，这一理论立场假设平行表示最终运动目标，而不是指定运动轨迹等方面的运动计划。解决这一争论的主要挑战是找到令人信服的措施，表明当前是否有多个运动计划(而不仅仅是目标)处于活动状态。我们在这里提出了一系列应对这一挑战的实验。为此，我们采用了运动目标和注意部署之间的良好关系。注意力被转移到一个或几个连续的运动目标上，这些目标在运动开始之前就已经存在，表现为与无关位置相比，目标位置的感知辨别能力增强。我们将这种实验方法扩展到探索手部伸展的多个运动目标的并行表征。最重要的是，我们探索了注意分配到轨迹定义的位置，例如障碍附近的区域，沿着潜在的相关运动轨迹。作为第二种方法，我们通过运动适应范式诱导出多个潜在相关的轨迹。最后，我们讨论运动方案选择的自上而下的方面，以阐明这些方面如何影响自下而上的感觉信息的平均。综上所述，拟议的实验将提供实质性和令人信服的证据，说明平行表征的基础是哪些运动规划水平。

Our environment constantly presents us with multiple opportunities and demands for action. At any given moment, we must select one of all possible actions, and specify the corresponding movement metrics. Evidence suggests that the brain simultaneously prepares multiple actions in parallel, and action selection results from continuous competition embedded in bottom-up driven sensorimotor processing that is biased by top-down decision-relevant information.However, there is ongoing debate about which aspects of actions are actually represented in parallel. Reaching trajectories of human participants usually reflect an average between the direct trajectories to several currently relevant targets; this aspect of motor behavior has been interpreted as indicating that the executed movement results from averaging of individual movement plans. This interpretation, thus, assumes that all aspects of the different actions are represented in parallel. However, averaging behavior appears to sometimes depend on strategic considerations. For instance, trajectory averaging is abandoned when targets are far apart, or when movements have to executed be very fast; this strategic behavior change improves participants’ overall performance. The use of such strategies has been taken to indicate that movement trajectories are not, by default, averaged. Instead, only a single detailed movement plan would be computed, and this single plan could be derived as an average when this is strategically advantageous. Thus, this theoretical stance assumes parallel representation of final movement goals, but not of movement plans that specify aspects such as the movement’s trajectory.The central challenge to solving this debate is to find convincing measures that indicate whether several movement plans (as opposed to just goals) are currently active. We propose here a series of experiments that address this challenge. To this end, we employ the well-established relationship between movement goals and attentional deployment. Attention is shifted towards one or several sequential motor goals already prior to movement initiation, expressed in enhanced perceptual discrimination performance at target as compared to irrelevant locations. We extend this experimental approach to probing the parallel representation of multiple motor goals for hand reaches. Critically, we probe the attentional deployment to trajectory-defining locations, such as regions near obstacles, along potentially relevant movement trajectories. As a second approach, we induce multiple potentially relevant trajectories through a motor adaptation paradigm. Finally, we address top-down aspects to motor plan selection to elucidate how such aspects affect the averaging of bottom-up sensory information. Together, the proposed experiments will provide substantive and cogent evidence about which levels of movement planning underlie parallel representation.