The effect of central and peripheral field stimulation on the rise time and gain of human optokinetic nystagmus

We wished to examine the spatial (gain) and temporal (rise time) properties of human optokinetic nystagmus (OKN) as a function of stimulus velocity and field location. Stimuli were either M-scaled random dots or vertical stripes that moved at velocities between 20-80 deg s(-1). Three field conditions were examined: full field; a 20 deg central field; and a 12.5 deg central-field mask. OKN gain was found to be significantly affected by stimulus velocity and stimulus location, with the higher stimulus velocities and the 12.5 deg central-field mask giving lower gains. Steady-state gains for all three field conditions were not found to be affected by prior adaptation to stationary or moving stimuli. The 63% rise time was found to be significantly affected by the stimulus velocity, whereas this was not the case for the 90% rise time. Neither rise time was found to be significantly affected by the field location. These results indicate that, although the effectiveness (gain) of peripheral retina is lower than that of the central retina during optokinetic stimulation, the peripheral retina has access to common mechanisms responsible for the fast component of OKN.     

The variable nature of cognitive control: a dual mechanisms framework

A core component of cognitive control - the ability to regulate thoughts and actions in accordance with internally represented behavioral goals - might be its intrinsic variability. In this article, I describe the dual mechanisms of control (DMC) framework, which postulates that this variability might arise from qualitative distinctions in temporal dynamics between proactive and reactive modes of control. Proactive control reflects the sustained and anticipatory maintenance of goal-relevant information within lateral prefrontal cortex (PFC) to enable optimal cognitive performance, whereas reactive control reflects transient stimulus-driven goal reactivation that recruits lateral PFC (plus a wider brain network) based on interference demands or episodic associations. I summarize recent research that demonstrates how the DMC framework provides a coherent explanation of three sources of cognitive control variation - intra-individual, inter-individual and between-groups - in terms of proactive versus reactive control biases.     

Evidence,explanation and enhanced indispensability

In this paper I shall adopt a possible reading of the notions of ‘explanatory indispensability’ and ‘genuine mathematical explanation in science’ on which the Enhanced Indispensability Argument (EIA) proposed by Alan Baker is based. Furthermore, I shall propose two examples of mathematical explanation in science and I shall show that, whether the EIA-partisans accept the reading I suggest, they are easily caught in a dilemma. To escape this dilemma they need to adopt some account of explanation and offer a plausible answer to the following ‘question of evidence’: What is a genuine mathematical explanation in empirical science and on what basis do we consider it as such? Finally, I shall suggest how a possible answer to the question of evidence might be given through a specific account of mathematical explanation in science. Nevertheless, the price of adopting this standpoint is that the genuineness of mathematical explanations of scientific facts turns out to be dependent on pragmatic constraints and therefore cannot be plugged in EIA and used to establish existential claims about mathematical objects.     

Mental-task instructions and optokinetic nystagmus to the left and right

The frequency of elicited optokinetic nystagmus (OKN) in both directions was studied in subjects instructed to perform mental tasks thought to be asociated primarily with either the right or left hemisphere or a combination of both. A negative relationship between OKN frequency and right-hemisphere activity was more strongly confirmed than the alternative hypotheses that OKN frequency would be negatively related to the total amount of inner processing or to the amount of visualization required by a task. A significantly higher frequency of OKN was elicited (in nonmyopic subjects) when the stripes were moving in the direction contralateral to the hemisphere presumably involved in the instructed mental task. Subjects showing higher rates of right lateral eye shift (in an interview situation) made greater adjustments in OKN frequency according to the nature of the mental task.     

Human optokinetic nystagmus: competition between stationary and moving displays

We reported earlier that occlusion of the central retina and stationary edges have highly interactive effects on the gain of optokinetic nystagmus (OKN; Murasugi, Howard, & Ohmi, 1986). In this study, we explored this effect in more detail. A central occluding band of variable height, flanked by vertical bars, was superimposed onto an array of dots moving at 30 degrees per second. The height of the occluding band required to abolish OKN increased with the separation of the vertical bars. For bars 3.5 degrees apart, OKN was abolished in most subjects when a band only 6' high ran between them. For bars 75 degrees apart, a band at least 20 degrees in height was required to abolish the response. The effects of the stationary figure depended to some extent on the subject's attention, but only at intermediate values of bar separation. Both low- and high-level mechanisms are proposed to account for the results.     

Explanatory Consolidation: From ‘Best’ to ‘Good Enough’

In science and everyday life, we often infer that something is true because it would explain some set of facts better than any other hypothesis we can think of. But what if we have reason to believe that there is a better way to explain these facts that we just haven’t thought of? Wouldn’t that undermine our warrant for believing the best available explanation? Many philosophers have assumed that we can solve such underconsideration problems by stipulating that a hypothesis should not only be ‘the best’ explanation available; rather, it should also be ‘good enough’. Unfortunately, however, the only current suggestion for what it might mean to say that an explanation is ‘good enough’ is, well, not good enough. This paper aims to provide a better account of what is required for an explanatory hypothesis to be considered ‘good enough’. In brief, the account holds that a ‘good enough’ hypothesis is one that has gone through a process that I call explanatory consolidation, in which accumulating evidence and failed attempts to formulate better alternatives gradually make it more plausible that the explanation we currently have is better than any other that could be formulated.     

Explaining in conversation: Towards an argument model

We examine the proposition that, in ordinary conversation, people are concerned to argue — to justify their claims and to counter potential and actual counter claims. We test out the proposition by analysing explanations in one particular conversation. We attend to the validity claims of what the speakers say, and to the authority with which they say it. Viewed in that light, we find that the majority of what might look like causal attributions turn out to look like argumentative claim-backings. We then go on to flesh out the quasi-pragmatic rules which might help to decide formally whether any given utterance is be er understood as an argument or a causal explanation. These rules revolve around the speaker's apparent intention and the projected relationship between the clauses in what she or he says. All of this takes us a fair way from attribution theory's model of explanation as the reporting of a cause, and we end up with an argumentative model of ordinary explanation.     

A Modulation Account of Negative Existentials

Fictional characters present a problem for semantic theorists. One approach to this problem has been to maintain realism regarding fictional characters, that is to claim that fictional characters exist. In this way names originating from fiction have designata. On this approach the problem of negative existentials is more pressing than it might otherwise be since an explanation must be given as to why we judge them true when the names occurring within them designate existing objects. So, realists must explain the intuitive truth of such statements. Some realists have appealed to pragmatics to explain this, but have not developed these positions fully. What follows is an original account of negative existentials based on the pragmatic process of modulation. Modulation affects the meaning of ‘exists’ such that its extension is merely those things that exist physically. It is then argued that the modulation approach provides a more natural account of the intuitive truth of negative existentials involving fictional characters than an account based on conversational implicatures. Finally, the modulation account is defended against objections presented against similar accounts.     

How affordances associated with a distractor object affect compatibility effects: A study with the computational model TRoPICALS

Seeing an object activates both visual and action codes in the brain. Crucial evidence supporting this view is the observation of object to response compatibility effects: perception of an object can facilitate or interfere with the execution of an action (e.g., grasping) even when the viewer has no intention of interacting with the object. TRoPICALS is a computational model that proposes some general principles about the brain mechanisms underlying compatibility effects, in particular the idea that top-down bias from prefrontal cortex, and whether it conflicts or not with the actions afforded by an object, plays a key role in such phenomena. Experiments on compatibility effects using a target and a distractor object show the usual positive compatibility effect of the target, but also an interesting negative compatibility effect of the distractor: responding with a grip compatible with the distractor size produces slower reaction times than the incompatible case. Here, we present an enhanced version of TRoPICALS that reproduces and explains these new results. This explanation is based on the idea that the prefrontal cortex plays a double role in its top-down guidance of action selection producing: (a) a positive bias in favour of the action requested by the experimental task; (b) a negative bias directed to inhibiting the action evoked by the distractor. The model also provides testable predictions on the possible consequences of damage to volitional circuits such as in Parkinsonian patients.     

基于预期理论的风险决策的神经机制

预期理论基于对期望效用理论的批判与发展,提出了价值函数与权重函数,对以往风险决策研究中所发现的现象进行了很好的预测与解释。预期理论的核心概念包括参照依赖、损失规避与权重函数。基于预期理论的一些决策偏差包括框架效应、禀赋效应和默认偏差也部分揭示了与人们风险决策有关的脑区。近年来,通过采用功能性核磁共振等脑成像手段对预期理论的一些核心成分进行的研究表明,涉及到人们风险决策的脑区主要有前额叶、纹状体、脑岛与杏仁核。未来的研究可以从预期理论的产生根源、个体发展以及遗传基因等角度进行进一步的探讨。     

On the failed institutionalization of German comparative psychology prior to 1940

Despite an illustrious history marked by the work of Wolfgang K?hler and Mathilde Hertz, among others-the significance of which still resonates in different fields of animal behavior research-and the fact that interesting work in the field continues, comparative psychology has no official status within German psychology. A partial explanation for this lack of official representation might derive from unsuccessful attempts historically to secure institutional status. "Gifted" animals served as much of the impetus for the beginning of a scientific animal psychology in Germany and contributed to its institutionalization by providing the incentive for the establishment of organizations dealing with animal psychology. Although initially serving as a catalyst for an interdisciplinary exchange on animal psychology, the case of Clever Hans was also exploited to help psychology gain institutional status in the field, albeit without lasting success.     

Attention level oscillations during visual perception of moving stimuli

Optokinetic nystagmus (OKN) pursuit phase velocity oscillations were studied in seven undergraduates during repeated 4 min presentation of optokinetic stimuli. The following variable parameters of the stimuli motion were used with each subject: horizontal direction, angular velocity (AV), and frequency-to-velocity ratio. AV of the OKN pursuit phases was found to decrease markedly within the first 30 sec of stimuli presentation with its successive increase and variously marked oscillations. Gradual decrease of the AV of OKN pursuit phases was observed at the end of the whole examination as compared to its beginning already within 4 min presentation of the moving stimuli. The results are discussed from the point of view of the arousal, and the activation components of visual attention.     

Localisation of auditory targets during optokinetic nystagmus

Previous studies have shown that the perceived location of visual stimuli briefly flashed during smooth pursuit, saccades, or optokinetic nystagmus (OKN) is not veridical. We investigated whether these mislocalisations can also be observed for brief auditory stimuli presented during OKN. Experiments were carried out in a lightproof sound-attenuated chamber. Participants performed eye movements elicited by visual stimuli. An auditory target (white noise) was presented for 5 ms. Our data clearly indicate that auditory targets are mislocalised during reflexive eye movements. OKN induces a shift of perceived location in the direction of the slow eye movement and is modulated in the temporal vicinity of the fast phase. The mislocalisation is stronger for look- as compared to stare-nystagmus. The size and temporal pattern of the observed mislocalisation are different from that found for visual targets. This suggests that different neural mechanisms are at play to integrate oculomotor signals and information on the spatial location of visual as well as auditory stimuli.     

The life and times of individuals scoring high and low on dispositional greed

Greed is a variable which might explain and predict a range of real-life criteria. Although often consulted as explanation in the public media, related scientific research has only recently begun. We approached greed from a personality psychology perspective regarding its nomological net and the prediction of theoretically related criteria. We found that a wide array of indicators, including behavior in economic games and risk games, as well as self-reported money investment and aimed at income, can be meaningfully predicted by dispositional greed, over and above the Big Five. Additionally, we found that dispositional greed is substantially related to psychopathy. According to our results, dispositional greed is an important variable which might explain unique variance with regard to theoretically related behaviors.     

Auditory repetition priming is impaired in pure alexic patients

Alexia without agraphia, or "pure" alexia, is an acquired impairment in reading that leaves writing skills intact. Repetition priming for visually presented words is diminished in pure alexia. However, it is not possible to verify whether this priming deficit is modality-specific or modality independent because reading abilities are compromised. Hence, auditory repetition priming was assessed with lexical decision and word stem completion tasks in pure alexic patients with lesions in left inferior temporal-occipital cortex and the splenium. Perceptually based, modality-specific priming models predict intact auditory priming, since auditory association cortex is spared in the patients. Alternatively, modality-independent models, which suggest that priming reflects the temporary modification of an amodal system, might predict impairments. Baseline performance was matched in the patients and controls, although lexical decision priming measures showed an interaction between group and repetition lag. The patients showed intact immediate priming but significantly less priming than controls at longer delays. Furthermore, word stem completion priming was abolished in the patients. One explanation for the deficit is that left inferior temporal-occipital cortex supports amodal aspects of priming, as suggested by recent neuroimaging results. Another possibility is that long-term auditory priming relies on covert orthographic representations which were unavailable in the patients. The results provide support for interactive models of word identification.     

A contrastive account of explanation generation

In this article, we propose a contrastive account of explanation generation. Though researchers have long wrestled with the concepts of explanation and understanding, as well as with the procedures by which we might evaluate explanations, less attention has been paid to the initial generation stages of explanation. Before an explainer can answer a question, he or she must come to some understanding of the explanandum—what the question is asking—and of the explanatory form and content called for by the context. Here candidate explanations are constructed to respond to the particular interpretation of the question, which, according to the pragmatic approach to explanation, is constrained by a contrast class—a set of related but nonoccurring alternatives to the topic that emerge from the surrounding context and the explainer’s prior knowledge. In this article, we suggest that generating an explanation involves two operations: one that homes in on an interpretation of the question, and a second one that locates an answer. We review empirical work that supports this account, consider the implications of these contrastive processes, and identify areas for future study.     

Effects of Soliciting Opinions on Contributions to a Public Good1

In a field study, subjects were mailed a request for a monetary contribution toward the maintenance of a public good. One half the subjects received only this request, while the other half received the request along with a short questionnaire that asked for subjects' opinions regarding how their contributions might be best put to use. It was predicted that subjects to whom questionnaires were sent, through enhanced perceptions of efficacy and ingroup identity, would contribute more money than subjects not given the opportunity to communicate their opinions The results, however, indicated that the manipulation had the reverse effect: subjects in the questionnaire condition contributed less money than subjects in the nequestionnaire condition. A post hoc explanation for the data based on the notion of “symbolic” helping actions is provided, and implications for solicitation programs and for research on social dilemmas are discussed.     

Developmental dissociation in the neural responses to simple multiplication and subtraction problems

Mastering single‐digit arithmetic during school years is commonly thought to depend upon an increasing reliance on verbally memorized facts. An alternative model, however, posits that fluency in single‐digit arithmetic might also be achieved via the increasing use of efficient calculation procedures. To test between these hypotheses, we used a cross‐sectional design to measure the neural activity associated with single‐digit subtraction and multiplication in 34 children from 2nd to 7th grade. The neural correlates of language and numerical processing were also identified in each child via localizer scans. Although multiplication and subtraction were undistinguishable in terms of behavior, we found a striking developmental dissociation in their neural correlates. First, we observed grade‐related increases of activity for multiplication, but not for subtraction, in a language‐related region of the left temporal cortex. Second, we found grade‐related increases of activity for subtraction, but not for multiplication, in a region of the right parietal cortex involved in the procedural manipulation of numerical quantities. The present results suggest that fluency in simple arithmetic in children may be achieved by both increasing reliance on verbal retrieval and by greater use of efficient quantity‐based procedures, depending on the operation.