RT patterns and chunks in SRT tasks: a reply to Jiménez (2008)

Previous research has shown that the formation of units or chunks contributes to sequence learning in serial reaction time (SRT) tasks (Koch & Hoffmann, Psychological Research 63:22–35, 2000). However, some of these results were assumed to be unrelated to sequence learning and to reflect preexistent response tendencies (Jiménez, Psychological Research 72:387–396, 2008). In the Experiment of this study, we aimed to evaluate this issue. One group of participants responded to a strongly structured sequence of digits by pressing one out of six response keys depending on digit identity. In a second experimental group, a weakly structured sequence was presented, which contained comparable transitions among the single items, but did not have series of ascending and descending triplets of successive digits. The results indicated that serial learning in general as well as response tendencies to certain fragments of the sequence were modulated by the manipulation of the strength of relational patterns. The data are consistent with the notion that relational patterns contribute to the formation of chunks as suggested in the original study.     

Exploiting redundancy for flexible behavior: unsupervised learning in a modular sensorimotor control architecture

Autonomously developing organisms face several challenges when learning reaching movements. First, motor control is learned unsupervised or self-supervised. Second, knowledge of sensorimotor contingencies is acquired in contexts in which action consequences unfold in time. Third, motor redundancies must be resolved. To solve all 3 of these problems, the authors propose a sensorimotor, unsupervised, redundancy-resolving control architecture (SURE_REACH), based on the ideomotor principle. Given a 3-degrees-of-freedom arm in a 2-dimensional environment, SURE_REACH encodes 2 spatial arm representations with neural population codes: a hand end-point coordinate space and an angular arm posture space. A posture memory solves the inverse kinematics problem by associating hand end-point neurons with neurons in posture space. An inverse sensorimotor model associates posture neurons with each other action-dependently. Together, population encoding, redundant posture memory, and the inverse sensorimotor model enable SURE_REACH to learn and represent sensorimotor grounded distance measures and to use dynamic programming to reach goals efficiently. The architecture not only solves the redundancy problem but also increases goal reaching flexibility, accounting for additional task constraints or realizing obstacle avoidance. While the spatial population codes resemble neurophysiological structures, the simulations confirm the flexibility and plausibility of the model by mimicking previously published data in arm-reaching tasks.     

What might philosophy of science look like if chemists built it?

Had more philosophers of science come from chemistry, their thinking would have been different. I begin by looking at a typical chemical paper, in which making something is the leitmotif, and conjecture/refutation is pretty much irrelevant. What in fact might have been, might be, different? The realism of chemists is reinforced by their remarkable ability to transform matter; they buy into reductionism where it serves them, but make no real use of it. Incommensurability is taken without a blink, and actually serves. The preeminence of synthesis in chemistry could have led philosophers of science to take more seriously questions of aesthetics within science, and to find a place in aesthetics for utility. The necessary motion twixt macroscopic and microscopic views of matter in modern chemistry leads to the coexistence of symbolic and iconic representations. And in another way to the deliberate, creative violation of categories.     

Global-local orientation congruency effects in visual search

In a visual search task, subjects had to decide which of 2 possible target letters was presented among 12 distractor letters. The 13 characters were arranged to form a global Navon-type letter. The global letter and the local letters (target and distractors) were independently presented in four different viewer-related orientations. When the global letter and the target were frequently congruently oriented, the response times increased with growing orientation disparity between them. This global-target congruency effect was independent from target identity (Experiment 1), and it diminished when global and target orientations were not correlated (Experiment 2). The results indicate that the orientation of the global letter can be deliberately used in order to facilitate the processing of congruently oriented local targets. The alignment of a spatial frame of reference is discussed as the most probable process underlying this facilitation.