A computer simulation model of rats’ place navigation in the Morris water maze

Rats rapidly learn to swim from a variety of starting locations, including novel ones, to a small invisible platform submerged in a pool of cool opaque liquid. A computer simulation based on a simple perceptual memory-matching model successfully mimics this ability. The model assumes that the rat, when it successfully reaches the platform, notes the distance to prominent extramaze landmarks and stores this perceptual information in memory. When placed in the pool on subsequent trials, the simulated rat attempts to match perceived distance between itself and the landmarks to the remembered distances from the platform to the landmark. The model accounts for many of the known facts about rats’ behavior in the swimming pool and makes some interesting predictions that could be easily tested experimentally. The model has the advantage, relative to other cognitive map models, of specifying how spatial information is represented in memory and how this information guides behavior.     

Does the radial arm maze necessarily test spatial memory?

Since its design 25 years ago (Olton & Samuelson, 1976), the eight-arm radial maze has become very popular and is now widely used to assess spatial memory in rodents. Two versions of the full-baited maze protocol are present in the literature: with or without confinement between the visit of each arm. The confinement was introduced by Olton himself as early as 1977 (Olton, Collison, & Werz, 1977) to eliminate stereotypic behaviors that he had previously observed. It is widely regarded that the confinement prevents rodents from developing these response patterns, and as such it is considered an improved procedure to test spatial memory. Surprisingly, to the best of our knowledge, no study has been especially designed to demonstrate the efficacy of the confinement in blocking the stereotypic behaviors of the animals. The present study compares the strategies of rats trained with or without a confinement procedure. The results show that, after nine days of training, rats submitted to a 5- or a 10-s confinement reach the same level of performance as rats without confinement. The confinement totally prevents stereotypic behaviors like clockwise serial searching strategies which are often observed without confinement. Even a 0-s confinement is sufficient to prevent clockwise strategies, but rats seem to develop other stratagems which do not imply spatial memory. Furthermore, rats previously trained without confinement are unable to perform the task when confinement is introduced on a test day. In contrast, rats previously trained with confinement perform the task correctly when the confinement is no longer present. Thus, without confinement, good levels of performance can be achieved without precise spatial representations.     

Does nondirectional signalization of target distance contribute to navigation in the Morris water maze?

The possibility that rats can navigate in the Morris water maze by reducing the difference between the memorized platform scene and the current sensory input was tested in nine blind rats. A computerized videosystem monitored the rats' movements in the pool and converted the rat-target distance into tones the frequency of which increased in 64 equal steps from 120 Hz at 128 cm to 7680 Hz at 0 cm. During 15 days of training to find a fixed platform position from different starting points (12 trials per day) average escape latencies decreased from 39.0 to 25.4 s. The performance significantly deteriorated when the acoustic distance signalization was omitted and/or when the target position was changed form trial to trial. It is concluded that blind rats solved the task by simultaneously employing search strategy based on position responses, mapping using acoustic background beacons, and distance reduction navigation. It is argued that the various strategies are additive and that their relative significance depends of the conditions of the experiment.     

Reconsidering the will to power in Heidegger's ‘Nietzsche’

In this paper, I reconsider Martin Heidegger's well-known interpretation of the Nietzschean conception of the will to power that emerges during the 1930s and 40s, focusing specifically on his conception of the will to power as the principle that suspends (or to use Heidegger's word, ‘permanentises’) becoming. After revealing the difficulties that this reading presents, I provide my own tentative interpretation of the doctrine. Specifically, I argue that Heidegger's opposition of the will to power and becoming cannot be sustained, and provide a so-called ‘strong’ reading of the will to power as an alternative.     

What’s the object of object working memory in infancy? Unraveling ‘what’ and ‘how many’

Infants have a bandwidth-limited object working memory (WM) that can both individuate and identify objects in a scene, (answering ‘how many?’ or ‘what?’, respectively). Studies of infants’ WM for objects have typically looked for limits on either ‘how many’ or ‘what’, yielding different estimates of infant capacity. Infants can keep track of about three individuals (regardless of identity), but appear to be much more limited in the number of specific identities they can recall. Why are the limits on ‘how many’ and ‘what’ different? Are the limits entirely separate, do they interact, or are they simply two different aspects of the same underlying limit?We sought to unravel these limits in a series of experiments which tested 9- and 12-month-olds’ WM for object identities under varying degrees of difficulty. In a violation-of-expectation looking-time task, we hid objects one at a time behind separate screens, and then probed infants’ WM for the shape identity of the penultimate object in the sequence. We manipulated the difficulty of the task by varying both the number of objects in hiding locations and the number of means by which infants could detect a shape change to the probed object. We found that 9-month-olds’ WM for identities was limited by the number of hiding locations: when the probed object was one of two objects hidden (one in each of two locations), 9-month-olds succeeded, and they did so even though they were given only one means to detect the change. However, when the probed object was one of three objects hidden (one in each of three locations), they failed, even when they were given two means to detect the shape change. Twelve-month-olds, by contrast, succeeded at the most difficult task level.Results show that WM for ‘how many’ and for ‘what’ are not entirely separate. Individuated objects are tracked relatively cheaply. Maintaining bindings between indexed objects and identifying featural information incurs a greater attentional/memory cost. This cost reduces with development. We conclude that infant WM supports a small number of featureless object representations that index the current locations of objects. These can have featural information bound to them, but only at substantial cost.     

‘Between the bridge and the brook’

Abstract

That suicide was a damnable sin in Reformation England has been emphasized so far in the historiography of self-killing, but in practice the clergy were equivocal over the question of whether all self-killers were damned. This article re-examines English Protestant beliefs about suicide and salvation from the mid-sixteenth to the mid-seventeenth century. It suggests that clerical statements about the damnableness of suicide need to be understood in the context of the threat posed by Stoic philosophy. Religious writers rejected the notion of noble suicide and reiterated Augustinian theology that premeditated self-killing was a form of murder. However, the harsh rhetoric was mitigated by a number of factors that brought into question the idea that all suicides were destined for Hell. These included changing medical opinion about mental states, evidence of the good character of many suicides, belief in the overpowering influence of demonic forces and basic Christian charity and compassion.     

On Failing to be Cartesian: Reconsidering the ‘Impurity’ of Descartes’s Meditation

Abstract

This paper begins from the observation that in the Meditations, Descartes never achieves the ‘pure’, thoroughly decontextualized kind of thinking he famously promoted. Some commentators have used this observation to promote pure inquiry more diligently and to criticize Descartes for failing to achieve it. Other commentators have simply called for greater historical fairness and urged that we renew our efforts to understand how Descartes’s inquiry actually does operate. This paper, although sympathetic with this second group of commentators, argues that in revisiting the tensions between what Descartes actually accomplished and what he said he was trying to accomplish, we should see a contemporary lesson, not just better historical understanding. It is argued that in spite of the strong presence in his writings of the imagery of the ‘Cartesian’ ideal of a perfectly presuppositionless philosophical standpoint, not only does Descartes himself never become a Cartesian, but his own practice provides perhaps the best evidence against the very possibility of the Cartesian ‘project of pure inquiry’ to which he aspired.     

Coding categorical and coordinate spatial relations in visual–spatial short-term memory

Four experiments explored the coding of categorical and coordinate spatial relations in visual–spatial short-term memory (VSSTM). Participants judged whether two stimuli presented successively on a computer screen were the same or different. On positional change trials the two stimuli differed in the position of one element. Positional changes were of two types, coordinate and categorical. On coordinate trials the position of one element changed by a small amount, but retained the categorical relationships (above, below, left of, right of) to all other elements. On categorical trials one element moved by the same amount but additionally changed its categorical relationship to one of the other elements (e.g., changed from below to above). Participants detected categorical changes more accurately than coordinate changes when the elements were independent locations marked by squares, indicating that the categorical relationships amongst the squares were encoded in memory. Furthermore, this categorical advantage was unmodulated by either the suppression of articulation (Experiment 2) or by the requirement to retain either colour–position associations or positions only (Experiment 3). When the elements to be remembered were the vertices of simple outline polygons (Experiment 4) there was no categorical advantage, establishing the effect as spatial in nature. Contrary to predictions derived from Postma and De Haan (1996) Postma, A. and De Haan, E. H. 1996. What was where? Memory for object locations. Quarterly Journal of Experimental Psychology, 49A: 178–199. [Crossref], [Web of Science ®] , [Google Scholar], the employment of categorical relations appears not to be specifically linked to either verbal coding or to the requirement to associate objects with positions. The results suggest that the categorical relations are an intrinsic property of the representation of spatial configurations.     

‘Necessity’ and ‘provability’ in the later wittgenstein

I present a new interpretation of Wittgenstein's later philosophy of logic and mathematics. This interpretation, like others, emphasizes Wittgenstein's attempt to reconcile platonistic and constructivistic approaches. But, unlike other interpretations, mine explains that attempt in terms of Wittgenstein's position about the relations between our concepts of necessity and provability. If what I say here is correct, then we can rescue Wittgenstein from the charge of naive relativism. For his relativism extends only to provability, and not to necessity.     

Immigrant residential geographies and the ‘spatial assimilation’ debate in Canada, 1997–2007

This paper discusses research published between 1997 and 2007 on the residential concentration of immigrants and ethnic and visible minority groups in Canadian metropolitan centres. Specifically, it reviews findings and conclusions that relate to the ongoing debate over the validity of assimilationist perspective assumptions regarding the typical social and spatial trajectory of newcomers. A Canadian immigrant underclass thesis is generally rejected, but some evidence emerges to suggest a potential bifurcation of the assumed pattern of sociospatial mobility. The traditional assumptions would hold for most groups, yet significant exceptions would justify an alteration of the model, essentially de-linking social from spatial mobility in the case of certain groups. Methodological considerations underlying this proposition are discussed.     

Philosophy and the ‘anteriority complex’

The project of naturalising phenomenology is examined within the larger context of the philosophy of science. Transcendental phenomenology, as defended by Husserl, in opposition to the naturalistic enterprise, reflects a particular way of thinking about philosophy and its relationship to the empirical sciences that stands as an obstacle to the project of naturalisation. This paper develops a critique of a basic assumption made in this conception of philosophy, namely that it is possible to ask and answer questions concerning knowledge in the abstract, prior to and independently of the various investigative contexts which are the immediate concern of practicing scientists. To successfully naturalise phenomenology, we need to abandon this conception of philosophy.     

Responsibility and the ‘Pie Fallacy’

Much of our ordinary thought and talk about responsibility exhibits what I call the ‘pie fallacy’—the fallacy of thinking that there is a fixed amount of responsibility for every outcome, to be distributed among all those, if any, who are responsible for it. The pie fallacy is a fallacy, I argue, because how responsible an agent is for some outcome is fully grounded in facts about the agent, the outcome and the relationships between them; it does not depend, in particular, on how responsible anyone else is for that same outcome. In this paper, I explore how the pie fallacy can arise by considering several different kinds of case in which two or more agents are responsible for the same outcome. I’ll end with some brief remarks on the potential consequences of my arguments for how to think about responsibility in war.

     

Can infant self-locomotion and spatial exploration predict spatial memory at school age?

According to an embodied view of development sensorimotor activity plays a central role in cognitive development. Following this idea, we studied whether the age of achieving self-locomotion milestones and spatial exploration during the first years of life predict spatial memory at (pre)school age. Spatial memory was assessed in 51 children at ages four and six years. Parents reported retrospectively about ages of attainment of self-locomotion milestones and about the children's spatial exploration behaviour during infancy and early toddlerhood. Results show that spatial exploration positively predicts spatial memory at both ages. The age of attainment of self- locomotion does not predict spatial memory at ages four and six. These findings extend previous work that showed a relation between exploration and spatial cognition over a short period of time. Results provide preliminary support to the hypothesis, suggesting that spatial exploration predicts spatial memory also over longer periods of time.     

On the Alleged Ambiguity of ‘Now’ and ‘Here’

It is argued that, in order to account for examples where the indexicals `now' and `here' do not refer to the time and location of the utterance, we do not have to assume (pace Quentin Smith) that they have different characters (reference-fixing rules), governed by a single metarule or metacharacter. The traditional, the fixed character view is defended: `now' and `here' always refer to the time and location of the utterance. It is shown that when their referent does not correspond to the time and/or location of the utterance, `now' and `here' work in an anaphoric way, inheriting their reference from another noun phrase. The latter may be explicit or implicit in the discourse. It is also shown that `now' and `here' can inherit their reference from a presupposed or tacit reference. In that case, they are coreferential with what will be labeled a `tacit initiator'. This anaphoric interpretation has the merit of fitting within the Kaplanian distinction between pure indexicals (`now', `here', `today', etc.) and demonstratives (`this', `that', `she', etc.).     

When do spatial and visual working memory interact?

This study examined how spatial working memory and visual (object) working memory interact, focusing on two related questions: First, can these systems function independently from one another? Second, under what conditions do they operate together? In a dual-task paradigm, participants attempted to remember locations in a spatial working memory task and colored objects in a visual working memory task. Memory for the locations and objects was subject to independent working memory storage limits, which indicates that spatial and visual working memory can function independently from one another. However, additional experiments revealed that spatial working memory and visual working memory interact in three memory contexts: when retaining (1) shapes, (2) integrated color-shape objects, and (3) colored objects at specific locations. These results suggest that spatial working memory is needed to bind colors and shapes into integrated object representations in visual working memory. Further, this study reveals a set of conditions in which spatial and visual working memory can be isolated from one another.     

Self-Knowledge and the ‘Inner Eye’

Mutual perceptual knowledge is a prevalent feature of our everyday lives, yet appears to be exceptionally difficult to characterise in an acceptable way. This paper argues for a renewed understanding of Stephen Schiffer's iterative approach to mutual knowledge, according to which mutual knowledge requires an infinite number of overlapping, embedded mental states. It is argued that the charge of ‘psychological implausibility’ that normally accompanies discussion of this approach can be offset by identifying mutual knowledge, not with the infinite iterations themselves, but with the finite base which Schiffer proves is capable of generating those iterations. An understanding of this finite base as a primitive, relational property holding between two or more people, allows us to understand the iterations as an implicit and ‘harmless’ intrapersonal feature of what is an interpersonal phenomenon. The paper concludes by relating the account to joint attention in infant interaction.