The influence of task characteristics on younger and older adult motor overflow

This study investigated the influence of attentional and motor demands on motor overflow in 17 healthy young (18–35 years) and 17 older adults (60–80 years). Participants performed a finger pressing task by exerting either 33% or 66% of their maximal force output using their dominant or nondominant hand. Overflow was concurrently recorded in the passive hand. Attention was manipulated via a tactile stimulus presented to one or both hands for certain trials. Results showed that older adults exhibited greater overflow than young adults and that the effect of target force was exacerbated in older adults. Further, only older adult overflow was increased when tactile stimulation was directed to one or both hands. Increased overflow in older adults may result from bilateral cortical activation that is influenced by increased task demands. To perform comparatively to younger adults, older adults may compensate for age-related brain changes by recruiting an increased cortical network.     

Semantic activation and letter search: Blocking or suppression?

Two experiments investigated associative priming with a letter-search prime task where either the prime and letter probe were presented simultaneously, or the letter probe appeared 200 ms (Experiment 1) or 300 ms (Experiment 2) after the prime. Weak associative priming was observed in both experiments, but unlike Stolz and Besner (1996) we found no evidence that priming was increased when the probe was delayed. However, strong associative priming was observed when a semantic decision had to be made on the prime (Experiment 3). Our results are consistent with an account where semantic activation of the prime occurs but its action on the target is suppressed by the prime task. The persistence of weak priming effects with the letter search task is explained in terms of the low-frequency items used.     

Mug handle affordance and automatic response inhibition: Behavioural and electrophysiological evidence

Behavioural evidence has shown that the perception of an object's handle automatically activates the corresponding action representation. The activation appears to be inhibited if the object is a task-irrelevant prime mug that is presented very briefly prior to responding to the target arrow. The present study uses an electrophysiological indicator of automatic response priming, the lateralized readiness potential (LRP), to investigate the mechanisms of this inhibition effect. We presumed that this effect would reflect motor self-inhibition processes. The self-inhibition explanation of the effect would assume that the effect reflects activation-followed-by-inhibition observed rapidly after the offset of the prime at the primary motor cortex. However, the results showed that the effect is not associated with modulation of the early LRP deflections. In contrast, the inhibition manifested itself in the later LRP deflections that we assume to be linked to interference in the processing of response-related aspects of the target. We propose that the LRP pattern is similar to what would be predicted from the negative priming explanation of the effect. The study sheds light on understanding inhibition mechanisms associated with automatically activated affordance representations.     

Are Automatic Imitation and Spatial Compatibility Mediated by Different Processes?

Automatic imitation or “imitative compatibility” is thought to be mediated by the mirror neuron system and to be a laboratory model of the motor mimicry that occurs spontaneously in naturalistic social interaction. Imitative compatibility and spatial compatibility effects are known to depend on different stimulus dimensions—body movement topography and relative spatial position. However, it is not yet clear whether these two types of stimulus–response compatibility effect are mediated by the same or different cognitive processes. We present an interactive activation model of imitative and spatial compatibility, based on a dual‐route architecture, which substantiates the view they are mediated by processes of the same kind. The model, which is in many ways a standard application of the interactive activation approach, simulates all key results of a recent study by Catmur and Heyes (2011) . Specifically, it captures the difference in the relative size of imitative and spatial compatibility effects; the lack of interaction when the imperative and irrelevant stimuli are presented simultaneously; the relative speed of responses in a quintile analysis when the imperative and irrelevant stimuli are presented simultaneously; and the different time courses of the compatibility effects when the imperative and irrelevant stimuli are presented asynchronously.     

Functional cerebral changes in multiple sclerosis patients during an autobiographical memory test

Our aim was to investigate the functional underpinnings of autobiographical memory (AM) impairment in multiple sclerosis (MS) patients. To that end, 18 patients and 18 controls underwent the autobiographical interview (AI). Subsequently, the 36 participants underwent a functional magnetic resonance imaging (fMRI) session designed to assess the construction and elaboration of AMs. A categorical control task was also presented. Patients were trained in the fMRI procedure to optimise the procedural aspects accompanying the task itself. Although the patients obtained significantly poorer AI scores (p < .001), their performance on the easier AM fMRI task was efficiently carried out, allowing relevant comparisons with healthy controls. Relatively to healthy controls, the patients showed increased and bilateral cerebral activations (p < .005) during the construction and elaboration phases. The prefrontal, temporal and posterior cerebral region activations were located within the core network sustaining AM, with the bilateral prefrontal region being centrally involved. The parametric neural responses to the difficulty of access and amount of details of memories were also significantly different for the two groups, with the right hippocampal region showing a particularly increased recruitment (p < .005). The findings suggested the presence of functional cerebral changes during AM performance and supported the presence of AM retrieval deficit in MS patients.     

On the Escaig obstacle hypothesis for cross-slip in face-centered-cubic materials

There is a significant body of literature wherein a linear approximation of Escaig's model is used to justify the large experimentally measured activation-volumes for cross-slip in face-centered-cubic copper. Here, by examining the error between the linear approximation and the original theory, we show that this explanation is not satisfactory. The calculated value for activation volume in copper, using Escaig's original equations, yields ～60b ³ (b?=?Burgers vector) while the linear approximation yields 200b ³, the latter result fortuitously matching the experimental values.     

Effects of Practice upon the Metabolic Cost of Mental Work

Two experiments with isopods, Armadillidium vulgare, were reported. In Experiment I, two groups of five Ss each learned to run a T maze to escape light and heat. Both original learning (OL), and relearning (RL) the next day, were to a criterion 9/10 correct. Between OL and RL one group was immobilized (I), and the other group was given the opportunity for activity (A). The I treatment resulted in greater savings on RL than did the A treatment, and it was thus concluded that A is a retroaction treatment. Experiment II was like I except that all Ss were extinguished immediately following OL, and then given either A or I until RL. In this experiment, the A treatment led to no savings, but the I treatment produced negative savings (more trials on RL relative to OL). It was concluded that the A treatment had retroactively interfered with extinction, and this result was discussed as analogous to differential spontaneous recovery in favor of the A group. It was concluded that Liberman's (4, 5) theory (that spontaneous recovery is due to the forgetting of extinction) is supported by the result of Experiment II.     

The Effect of Phonological Structure on Visual Word Access in Bilinguals

Two experiments examined if visual word access varies cross-linguistically by studying Spanish/English adult bilinguals, priming two syllable CVCV words both within (Experiment 1) and across (Experiment 2) syllable boundaries in the two languages. Spanish readers accessed more first syllables based on within syllable primes compared to English readers. In contrast, syllable-based primes helped English readers recognize more words than in Spanish, suggesting that experienced English readers activate a larger unit in the initial stages of word recognition. Primes spanning the syllable boundary affected readers of both languages in similar ways. In this priming context, primes that did not span the syllable boundary helped Spanish readers recognize more syllables, while English readers identified more words, further confirming the importance of the syllable in Spanish and suggesting a larger unit in English. Overall, the experiments provide evidence that readers use different units in accessing words in the two languages.     

Interaction Between Phonological and Semantic Representations: Time Matters

Computational modeling and eye‐tracking were used to investigate how phonological and semantic information interact to influence the time course of spoken word recognition. We extended our recent models (Chen & Mirman, 2012; Mirman, Britt, & Chen, 2013) to account for new evidence that competition among phonological neighbors influences activation of semantically related concepts during spoken word recognition (Apfelbaum, Blumstein, & McMurray, 2011). The model made a novel prediction: Semantic input modulates the effect of phonological neighbors on target word processing, producing an approximately inverted‐U‐shaped pattern with a high phonological density advantage at an intermediate level of semantic input—in contrast to the typical disadvantage for high phonological density words in spoken word recognition. This prediction was confirmed with a new analysis of the Apfelbaum et al. data and in a visual world paradigm experiment with preview duration serving as a manipulation of strength of semantic input. These results are consistent with our previous claim that strongly active neighbors produce net inhibitory effects and weakly active neighbors produce net facilitative effects.