The effect of response competition on functional hemispheric asymmetries for global/local processing

It is widely assumed that the cerebral hemispheres differ in their capacity for processing the global and local levels of hierarchical stimuli. However, corresponding visual-field (VF) effects in response time studies did not show up under all circumstances. In the present article the role of response conflict between the levels for the occurrence of these effects is investigated. Three experiments with hierarchical letters are reported, in which the absolute and/or the relative interference between the stimulus levels was varied. It turned out that VF effects occurred only for conflicting stimuli and only when there was at least a certain amount of absolute interference, whereas variations of the relative interference had no effect in this respect. These results suggest that there is a qualitative relationship between interference and VF effects. A possible explanation is provided by the assumption that the hemispheres are functionally equivalent with respect to early stimulus representations, whereas they differ in their efficiency for integrating letter identity and stimulus level.     

Personal names and the human right hemisphere: an illusory link?

Names are thought to be represented in the brain differently from common nouns. Although this idea is supported by both theoretical and empirical arguments, the brain areas that are relevant for the recognition of personal names-and in particular the extent of right hemisphere involvement-remain controversial. We investigated the hypothesis that, unlike common nouns, personal names are represented preferentially by the right hemisphere (D. Van Lancker, 1991; D. Van Lancker et al., 1991; C. Ohnesorge & D. Van Lancker, 1999). Participants performed lexical decisions to common nouns and pseudowords (Experiment 1) or familiarity decisions to personal names (Experiment 2), which were presented briefly to the left or right visual fields. Asymmetries were small or absent for both pseudowords and unfamiliar names. For familiar names, both reaction times and error rates revealed strong advantages for the right visual field/left hemisphere (RVF/LH), which were comparable to the asymmetries for nouns. Familiar personal names may be represented by brain systems that differ from those representing common nouns, but current evidence does not suggest a distinct contribution of the right hemisphere to these brain systems.     

About the relationship between basic numerical processing and arithmetics in early Alzheimer's disease--a follow-up study

We studied the relationship between basic numerical knowledge and arithmetics (facts and procedures) in early Alzheimer's Disease (AD). In most patients, basic numerical knowledge was found to be preserved, as reflected by low error rates, distance effect in number comparison, and subitizing in naming numerosities. However, within arithmetics, AD patients exhibited decreased fact and procedural knowledge. Interestingly, double dissociations were found not only between facts and procedures but also between basic numerical knowledge and arithmetics. Thus, our results suggest that basic numerical knowledge need not be a prerequisite for the maintenance of arithmetics, but rather corroborate calculation models that postulate the functional independence of its components. Further, we found patient specific error types which might serve to identify early AD. The follow-up about one year later indicated significant qualitative, but only marginal quantitative performance changes.     

Hindsight bias around the world

Hindsight bias refers to the tendency to overestimate in hindsight what one has known in foresight. Recently, two experiments extended the research to include samples from different cultures (Choi & Nisbett, 2000; Heine & Lehman, 1996). Asking their participants what they would have guessed before they knew the outcome ("hypothetical design"), Choi and Nisbett (2000) found that Koreans, in comparison to North Americans, exhibited more hindsight bias. Heine and Lehman (1996), however, reported that Japanese people in comparison to Canadians showed marginally less hindsight bias. In a second study, in which participants were asked to recall what they had estimated before they knew the outcome ("memory design"), the latter authors found no difference in hindsight bias between Japanese people and Canadians. We extended these studies with 225 Internet participants, in a hypothetical design, from four different continents (Asia, Australia, Europe, and North America). Hindsight bias was large and similar for all samples except for German and Dutch participants who showed no hindsight bias at all. While the latter effect may be based on peculiarities of the material and of the participants, the former underscores the worldwide stability of the phenomenon. In addition a follow-up surprise rating (paper and pencil) in China (35 participants) and Germany (20 participants) revealed that only less surprising items led to hindsight bias while more surprising ones did not. We suggest that the basic cognitive processes leading to hindsight bias are by-products of the evolutionary-evolved capacity of adaptive learning. On top of these basic processes, individual meta-cognitions (e.g., elicited by surprise) or motives (e.g., a self-serving motive) may further moderate the amount of bias, thus explaining the diverging results of Choi and Nisbett (2000), Heine and Lehman (1996), and our own study.     

Acquisition and use of mental operators: effects of type of practice

Planning interactions with the physical world requires knowledge about operations; in short, mental operators. Abstractness of content and directionality of access are two important properties to characterize the representational units of this kind of knowledge. Combining these properties allows four classes of knowledge units to be distinguished that can be found in the literature: (a) rules, (b) mental models or schemata, (c) instances, and (d) episodes or chunks. The influence of practicing alphabet-arithmetic operators in a prognostic, diagnostic, or retrognostic way (A + 2 = ?, A? = C, or ? + 2 = C, respectively) on the use of that knowledge in a subsequent test was used to assess the importance of these dimensions. At the beginning, the retrognostic use of knowledge was worse than the prognostic use, although identical operations were involved (A + 2 = ? vs. ? - 2 = A). This disadvantage was reduced with increased practice. Test performance was best if the task and the letter pairs were the same as in the acquisition phase. Overall, the findings support theories proposing multiple representational units of mental operators. The disadvantage for the retrognosis task was recovered in the test phase, and may be evidence for the importance of the order of events independent of the order of experience.     

Speech perception deficits in Parkinson's disease: underestimation of time intervals compromises identification of durational phonetic contrasts

Besides motor, vegetative, and cognitive signs, patients suffering from Parkinson's disease (PD) may show distinct perceptual deficits such as underestimation of time intervals extending across several seconds. Assuming this impairment also to affect the domain of tens of milliseconds, disrupted encoding of the acoustic speech signal with respect to segment durations conveying linguistic information must be expected. To test this hypothesis, 10 PD patients and matched controls performed an identification task using a series of 10 stimuli derived from the utterance "Boten" (/bo:tn/, 'messengers'; produced with nasal plosion) by exclusive manipulation of occlusion length (110-20 ms in steps of 10 ms). Under these conditions, word-medial silence cues the voicing category of the respective stop consonant. Seven PD subjects showed normal identification curves, i.e., categorized the shortest and longest stimuli with high probability each as the minimal pair cognates "Boden" and "Boten," respectively. In contrast, the remaining three patients labeled all items across the complete range of occlusion lengths as "Boden." A subsequent experiment found a horizontal shift of the identification curves toward larger signal durations (> 120 ms) in these three subjects. Bilateral cerebellar degeneration has been found to yield a different response pattern, i.e., near-chance level of performance. Considering recent information-processing models of scalar interval timing, striatal disorders seem to slow down an oscillatory pacemaker, whereas cerebellar dysfunctions may impair comparison of measured durations with stored reference memory traces.     

Visual search for dimensionally redundant pop-out targets: evidence for parallel-coactive processing of dimensions

In two visual search experiments, the detection of singleton feature targets redundantly defined on multiple dimensions was investigated. Targets differed from the distractors in orientation, color, or both (redundant targets). In Experiment 1, the various target types were presented either in separate blocks or in random order within blocks. Reaction times to redundant targets significantly violated the race model inequality (Miller, 1982), but only when there was constancy of the target-defining dimension(s) within trial blocks. In Experiment 2, there was dimensional variability within blocks. Consistent with Experiment 1, constancy of the target-defining dimension(s), but this time across successive trials (rather than within blocks), was critical for observing violations of the race model inequality. These results provide evidence for parallel-coactive processing of multiple dimensions, consistent with the dimension-weighting account of Müller, Heller, and Ziegler (1995).     

Brain-computer communication: unlocking the locked in

With the increasing efficiency of life-support systems and better intensive care, more patients survive severe injuries of the brain and spinal cord. Many of these patients experience locked-in syndrome: The active mind is locked in a paralyzed body. Consequently, communication is extremely restricted or impossible. A muscle-independent communication channel overcomes this problem and is realized through a brain-computer interface, a direct connection between brain and computer. The number of technically elaborated brain-computer interfaces is in contrast with the number of systems used in the daily life of locked-in patients. It is hypothesized that a profound knowledge and consideration of psychological principles are necessary to make brain-computer interfaces feasible for locked-in patients.     

Time course of the blindness to response-compatible stimuli

This article examines the time course of a deficit in identifying a stimulus sharing a compatible feature with a response that is executed in parallel ("blindness to response-compatible stimuli," J. Müsseler & B. Hommel, 1997a). In 5 experiments, participants performed a timed response, and the presentation point of time of a to-be-identified stimulus was varied in respect to response execution. A blindness effect was observed when the stimulus was presented between response cue offset and response execution. In contrast, the identification of a stimulus presented before the response cue or after response execution was not affected by stimulus-response compatibility--a finding that rules out a retention-based explanation. These results support an explanation that states that the perceptual processing of a stimulus feature is impaired as long as the shared perception-action feature code is integrated into the representation of a to-be-executed response.