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We report the case of a 48 year old men who developed a selective impairment in famous voice recognition after ischemic stroke in right subcortical structures (lenticular nucleus and head of the caudate) and right anterior temporal lobe. He underwent fibrinolytic treatment. During the following days he progressively recovered and was discharged without neurological focal sign. Patent foramen ovale was found. When he got back to his house he noticed that he was unable to recognize the voice of his favoured singers and needed to ask who was the singer to his relatives. Neuropsychological examination revealed a selective impairment in famous voice recognition in the absence of alteration of voice perception, face perception and famous face recognition. All other neuropsychological domains were spared. In particular language, memory and executive functions were intact. Neuroimaging carried out by means of PET and MRI revealed two small ischemic lesions in the right subcortical region, involving lenticular and caudate nuclei and in the right temporal pole. To our knowledge, this is the first case described in literature of a patient showing a selective associative phonagnosia after right anterior temporal stroke. The present case helps to clarify the brain circuits underlying famous voice recognition and adds evidence in favour of a right hemisphere involvement in processing knowledge of familiar voices. These findings are discussed in relation to current models of brain organization of person-specific and general semantic knowledge.

Bilinguals require a high degree of cognitive control to select the language intended for speaking and inhibit the unintended. Previous neuroimaging studies have not teased apart brain regions for generating the intention to use a given language, and those for speaking in that language. Separating these two phases can clarify at what stage competition between languages occurs. In this fMRI study German-English bilinguals were first cued to use German or English. After a delay, they named a picture in the cued language. During the intention phase, the precuneus, right superior lateral parietal lobule, and middle temporal gyrus were more activated when participants had to update the currently active language. During language execution activation was higher for English compared to German in brain areas associated with cognitive control, most notably the anterior cingulate and the caudate. Our results suggest two different systems enabling cognitive control during bilingual language production.

In recent years multivariate decoding has allowed to test where and how mental representations can be decoded from neuroimaging signals, which sheds light on how these representations are encoded in the brain. In one line of experiments, we investigated how intentions are encoded in fMRI signals, thus revealing information in medial and lateral prefrontal regions. These informative neural representations were even present prior to the person's awareness of their chosen intention. In comparison, for cued intentions we found information predominantly in lateral, but not medial prefrontal cortex. Intention coding in prefrontal cortex followed a compositional code and could also be observed across extended delays during which participants were busy performing other tasks. Taken together, our results suggest a systematic, compositional and hierarchical code in prefrontal cortex which intentions are encoded across delays while the mind is busy working on other tasks.

A defi ning trait of cognition is the capacity to combine information into compound concepts. This ability relies, among others, on the logical connectives ‘and’, ‘or’ and ‘if-then’. Simple sentences, such as “there is a fork on the table” (A) or “there is a knife” (B), can be combined in different ways using different connectives. No evidence is available to date on how and where the brain represents different concept combinations produced by different connectives, and how these are evaluated against new facts. Here, participants learned associations between graphic cues and conjunctive (A and B), disjunctive (A or B) or conditional (If A then B) sentences. During fMRI scanning, a cue was presented, followed by a delay, during which participants had to represent the sentence associated to the cue; fi nally, a visual scene had to be evaluated for compatibility with the sentence. Two participant groups were recruited so that conditionals (If A then B) were interpreted in either of two alternative ways (thus, same form, different semantics). Multivariate decoding applied to the delay period revealed that the active sentence was encoded in left inferior frontal gyrus (BA44). During the delay, no difference was found between participant groups. During the target phase, we found higher activations in rostral regions of left inferior frontal cortex (BA47), for disjunctions and conditionals relative to conjunctions. Activation of the inferior parietal lobe only was modulated by the interpretation of conditionals.

Semantic fluency is widely used both as a clinical test and as a basic tool for understanding how humans extract information from the semantic store. Recently, major efforts have been made to devise fine-grained scoring procedures to measure the multiple cognitive processes underlying fluency performance. Nevertheless, it is still unclear how many and which independent components are necessary to thoroughly describe performance on the fluency task. Furthermore, whether a combination of multiple indices can improve the diagnostic performance of the test should be assessed. In this study, we extracted multiple indices of performance on the semantic fluency test from a large sample of healthy controls (n = 307) and patients (n = 145) suffering from three types of focal dementia or Alzheimer's Disease (AD). We found that five independent components underlie semantic fluency performance. We argue that these components functionally map onto the generation and application of a search strategy (component 2), to the monitoring of the overall sequence to avoid repetitions (component 3) and out-of-category items (component 4), and to the full integrity of the semantic store (component 5). The integrated and effective work of all these components would relate to a “general effectiveness” component (component 1). Importantly, while all the focal dementia groups were equally impaired on general effectiveness measures, they showed differential patterns of failure in the other components. This finding suggests that the cognitive deficit that impairs fluency differs among the three focal dementia groups: a semantic store deficit in the semantic variant of primary progressive aphasia (sv-PPA), a strategy deficit in the non-fluent variant of primary progressive aphasia (nfv-PPA), and an initiation deficit in the behavioural variant of fronto-temporal dementia (bv-FTD). Finally, we showed that the concurrent use of multiple fluency indices improves the diagnostic accuracy of semantic f

In everyday life, humans use rules to organize their thoughts and actions in order to achieve specific goals (Bunge & Wallis, 2007). For simple situations, single rules can be used to link a sensory stimulus (the traffic light is green) to its appropriate response (cross the road). More complex situations, however, require the application of multiple rules organized in hierarchies, where high level rules influence the selection or application of lower level rules. Previous studies have demonstrated that Prefrontal Cortex (PFC) is one of the key areas underlying rule processing and control of action. However, it is still unclear whether distinct brain regions within PFC systematically encode qualitatively different task features. In the present study we investigated whether different features defining a complex rule set are represented in different brain areas depending on the level of control they enforce. To this purpose, we devised an experiment in which participants (N = 20) learnt complex rule sets composed by rules at two different levels of control: low (e.g., “if you see a banana, then press left”) and high (e.g., “If you see a star, then only consider red targets”). The task required participants to retrieve, maintain, and apply two rule sets (one low and one high level) to target stimuli. At the beginning of each trial two cues associated with low (or high) level rules were displayed, followed by a delay (delay 1). Then a second pair of cues standing for high (or low) level rules were presented followed by a second delay (delay 2), after which the target was shown. Participants had to apply all the rules to the target stimuli and respond accordingly. The paradigm allowed us to: (i) independently assess the encoding of high and low level rules, (ii) evaluate the difference between the encoding of the two types of rules (comparing high vs. low level rule representations during delay 1, when only one type of rule was maintained), and (iii) decode rule integrat

Nella vita quotidiana è frequente l’utilizzo di regole per organizzare pensieri ed azioni al fine di raggiungere obiettivi prefissati. Per le situazioni più semplici, singole regole condizionali (“se... allora...”) sono sufficienti. Situazioni più complesse, tuttavia, richiedono la considerazione contemporanea di molteplici regole, organizzate sia in termini temporali che gerarchici. Studi precedenti hanno dimostrato che la corteccia prefrontale (PFC) laterale è una delle aree critiche per la rappresentazione di regole semplici. Rimane da chiarire tuttavia dove e come il nostro cervello rappresenti insiemi di regole più complessi. Abbiamo condotto quattro esperimenti, manipolando lo stesso paradigma di base. I soggetti sono preliminarmente istruiti a rappresentare e applicare più insiemi di regole. Le regole utilizzate nei diversi esperimenti si collocano a diversi livelli di complessità. In ciascuna prova sperimentale i soggetti devono rievocare, rappresentare e quindi applicare uno degli insiemi di regole appresi. I soggetti sono sottoposti a scansione fMRI. I dati sono analizzati con tecniche multivariate per identificare quali aree cerebrali siano coinvolte nella rappresentazione di specifiche regole. Dalle analisi è emerso, come atteso, che la PFC laterale è coinvolta nella rappresentazione di regole. E’ inoltre emerso come informazioni relative a un'unica regola complessa non siano rappresentate tutte nella stessa regione cerebrale. Al contrario, le diverse caratteristiche che concorrono a costruire una regola complessa sono ripartite in aree cerebrali diverse, in funzione del tipo di informazione da rappresentare. I risultati della nostra serie sperimentale suggeriscono che la rappresentazione di regole complesse è “composizionale”. Gli elementi base delle regole complesse sono identificati e rappresentati separatamente dal nostro cervello. La segregazione dell’informazione avviene in aree cerebrali appropriate alla tipologia di contenuto da rappres

Humans are able to flexibly devise and implement rules to reach their desired goals. For simple situations, we can use single rules, such as "if traffic light is green then cross the street." In most cases, however, more complex rule sets are required, involving the integration of multiple layers of control. Although it has been shown that prefrontal cortex is important for rule representation, it has remained unclear how the brain encodes more complex rule sets. Here, we investigate how the brain represents the order in which different parts of a rule set are evaluated. Participants had to follow compound rule sets that involved the concurrent application of two single rules in a specific order, where one of the rules always had to be evaluated first. The rules and their assigned order were independently manipulated. By applying multivariate decoding to fMRI data, we found that the identity of the current rule was encoded in a frontostriatal network involving right ventrolateral prefrontal cortex, right superior frontal gyrus, and dorsal striatum. In contrast, rule order could be decoded in the dorsal striatum and in the right premotor cortex. The nonhomogeneous distribution of information across brain areas was confirmed by follow-up analyses focused on relevant regions of interest. We argue that the brain encodes complex rule sets by "decomposing" them in their constituent features, which are represented in different brain areas, according to the aspect of information to be maintained.

We investigated whether two basic forms of deductive inference, Modus Ponens and Disjunctive Syllogism, occur automatically and without awareness. In Experiment 1, we used a priming paradigm with a set of conditional and disjunctive problems. For each trial, two premises were shown. The second premise was presented at a rate designed to be undetectable. After each problem, participants had to evaluate whether a newly-presented target number was odd or even. The target number matched or did not match a conclusion endorsed by the two previous premises. We found that when the target matched the conclusion of a Modus Ponens inference, the evaluation of the target number was reliably faster than baseline even when participants reported that they were not aware of the second premise. This priming effect did not occur for any other valid or invalid inference that we tested, including the Disjunctive Syllogism. In Experiment 2, we used a forced-choice paradigm in which we found that some participants were able to access some information on the second premise when their attention was explicitly directed to it. In Experiment 3, we showed that the priming effect for Modus Ponens was present also in subjects who could not access any information about P(2). In Experiment 4 we explored whether spatial relations (e.g., "a before b") or sentences with quantifiers (e.g., "all a with b") could generate a priming effect similar to the one observed for Modus Ponens. A priming effect could be found for Modus Ponens only, but not for the other relations tested. These findings show that the Modus Ponens inference, in contrast to other deductive inferences, can be carried out automatically and unconsciously. Furthermore, our findings suggest that critical deductive inference schemata can be included in the range of high-level cognitive activities that are carried out unconsciously.

Several studies have shown that watching one’s own body part improves tactile acuity and discrimination abilities for stimuli presented on that location. In our experiment we asked the participants to localize tactile stimuli presented on the left or right arm. During the task the participants were not allowed to watch their body, but they could see another person’s left arm via a LCD display. This arm could be touched or not during the presentation of the tactile stimuli. We found that when the participants saw a finger touching the arm on the screen, their responses to the tactile stimuli presented on the left and on the right arm were faster than when the arm on the screen was approached but not touched. Critically, we did not find any illusion of ownership related to the hand seen on the screen. We concluded that the effects found might be mediated by higher order multisensory mechanisms related to the allocation of attentional resources to the body.

Deduction is the ability to draw necessary conclusions from previous knowledge. Here we propose a novel approach to understanding the neural basis of deduction, which exploits fine-grained inter-participant variability in such tasks. Participants solved deductive problems and were grouped by the behavioral strategies employed, i.e., whether they were sensitive to the logical form of syllogistic premises, whether the problems were solved correctly, and whether heuristic strategies were employed. Differential profiles of neural activity can predict membership of the first two of these groups. The predictive power of activity profiles is distributed non-uniformly across the brain areas activated by deduction. Activation in left ventro-lateral frontal (BA47) and lateral occipital (BA19) cortices predicts whether logically valid solutions are sought. Activation of left inferior lateral frontal (BA44/45) and superior medial frontal (BA6/8) cortices predicts sensitivity to the logical structure of problems. No specific pattern of activation was associated with the use of a non-logical heuristic strategy. Not only do these findings corroborate the hypothesis that left BA47, BA44/45 and BA6/8 are critical for making syllogistic deductions, but they also imply that they have different functional roles as components of a dedicated network. We propose that BA44/45 and BA6/8 are involved in the extraction and representation of the formal structure of a problem, while BA47 is involved in the selection and application of relevant inferential rules. Finally, our findings suggest that deductive reasoning can be best described as a cascade of cognitive processes requiring the concerted operation of several, functionally distinct, brain areas.

Conditional rules of the form "if x then y" are of vital importance for our everyday life. Recent research has started to investigate the neural substrate underlying conditional rule processing. A critical aspect of rule processing that has so far been neglected is that many situations require the rules to be executed in a specific order. For example, it might be wise to apply the rule “If you don't have any money, go to the ATM machine” BEFORE the rule “If you want ice-cream, go to the ice-cream shop”, instead of applying them vice versa. Here, we present the results from a functional magnetic resonance imaging (fMRI) study in which we successfully decoded the identity of two simultaneously active rules as well as their application order from local patterns of fMRI data. A modified cued task-switching paradigm was administered during fMRI scanning. Participants were required to retrieve, maintain, and apply two conditional rules (e.g. “First, if there is a musical instrument, press left. Second, if there is a food item, press right”) to a set of target stimuli. We identified regions containing representations of rule identity and application order by applying multivariate pattern classifiers on local patterns of activation during the delay period between cue presentation and task execution. Using a redundant coding scheme for the rules (each rule was alternatively represented by one of two visual cues in different trials), we were able to disentangle representations of rules and representations of visual features of the cue. Representations of rule identity were found in bilateral supero-lateral parietal cortices, right dorso-lateral prefrontal cortex (dlPFC), and right anterior cingulate cortex (ACC). Representations of application order were found in bilateral supero-lateral parietal cortices and right ACC. In ACC, we found an overlap between regions that contained representations of rules and rule order. In contrast, a dissociation between both regions was found

We investigated whether a basic deductive inference, namely the modus ponens, is an automatic processing step carried out even in the absence of willingness to reason and awareness of all the premises. We used an exhaustive set of conditional problems concerning numbers, with a subliminal second premise, followed by a target number. Participants evaluated whether the target number was odd or even. The target number could match or not match a valid conclusion endorsed by the premises. We found that evaluations of target numbers matching the conclusion of a modus ponens were faster than the evaluations of numbers following all other types of problems. This finding shows that modus ponens is automatic and can be triggered by subliminal stimuli.

Elementary deduction is the ability of unreflectively drawing conclusions from explicit or implicit premises, on the basis of their logical forms. This ability is involved in many aspects of human cognition and interactions. To date, limited evidence exists on its cortical bases. We propose a model of elementary deduction in which logical inferences, memory, and meta-logical control are separable subcomponents. We explore deficits in patients with left, medial and right frontal lesions, by both studying patients' deductive abilities and providing measures of their meta-logical sensitivity for proof difficulty. We show that lesions to left lateral and medial frontal cortex impair abilities at solving elementary deductive problems, but not so lesions to right frontal cortex. Furthermore, we show that memory deficits differentially affect patients according to the locus of the lesion. Left lateral patients with working memory deficits had defective deductive abilities, but not so left lateral patients with spared working memory. In contrast, in medial patients both deductive and meta-deductive abilities were affected regardless of the presence of memory deficits. Overall, the results are compatible with a componential view of elementary deduction, and call for the elaboration of more fine-grained models of deductive abilities

Two experiments investigated whether dealing with a homogeneous subset of syllogisms with time-constrained responses encouraged participants to develop and use heuristics for abstract (Experiment 1) and thematic (Experiment 2) syllogisms. An atmosphere-based heuristic accounted for most responses with both abstract and thematic syllogisms. With thematic syllogisms, a weaker effect of a belief heuristic was also observed, mainly where the correct response was inconsistent with the atmosphere of the premises. Analytic processes appear to have played little role in the time-constrained condition, whereas their involvement increased in a self-paced, unconstrained condition. From a dual-process perspective, the results further specify how task demands affect the recruitment of heuristic and analytic systems of reasoning. Because the syllogisms and experimental procedure were the same as those used in a previous neuroimaging study by Goel, Buchel, Frith, and Dolan (2000), the result also deepen our understanding of the cognitive processes investigated by that study

In the present paper we report the performance on object use and on semantic tasks of two patients, D.L. with probable semantic dementia, and A.M. with an atypical onset of dementia of Alzheimer, assessed twice two years apart. In particular, we investigated whether the patients' ability to use objects degraded as a function of their semantic knowledge about those objects. Results from the two assessments in 2002 and in 2004 confirmed that both patients had a selective loss of the lexical-semantic knowledge, despite a relative preservation of the other cognitive abilities including object use. This pattern of results suggests that semantic knowledge is not necessarily involved in the correct use of objects.

In everyday life, people untrained in formal logic draw simple deductive inferences from linguistic material (i.e., elementary propositional deductions). Presently, we have limited information on the brain areas implicated when such conclusions are drawn. We used event-related fMRI to identify these brain areas. A set of multiple and independent criteria was derived from the two main theories in the field of reasoning to maximize the reliability of detection of areas in which activity is specifically associated with deductive inferences. Two left lateralized clusters of areas, one in frontal cortex (Brodmann Area 44 and 6) and one in parietal lobe (BA 40), satisfied all criteria; activation was present at the moment of inference, it was shared by both conditional ("if-based") and disjunctive ("or-based") inferences but was greater for disjunctive clauses. Identification of the reasoning network was corroborated by the observation that activity in these areas was greater the longer the reasoning time. Taken together with results from preceding studies, our findings suggest possible theoretically relevant dissociations between elementary propositional deductions and other types of deductive reasoning.

Semantic verbal fluency is widely used in clinical and experimental studies. This task is highly sensitive to the presence of brain pathology and is frequently impaired after frontal lesions. Besides the total number of words generated, a qualitative analysis of their sequence can add valuable information about the impaired cognitive components. Thirty-four frontal patients and a group of matched controls were examined. Besides the number of words and subcategories retrieved by each group, we analysed two distinct aspects of the word sequence: the search strategy through a semantically organised store and the ability to switch from one subcategory to another. We checked whether the pattern of impairment changed according to the lesion site within the frontal lobe. Overall, patients produced fewer words than controls. However, only lateral frontal patients presented a reduced semantic relatedness between contiguously produced words and a specifically increased proportion of switches to different subcategories. The performance of lateral frontal patients was in line with the hypothesis of a search strategy impairment and cannot be attributed to a switching deficit. The performance of mesial frontal patients could be ascribed to a general deficit of activation

This study tested the impact of prefrontal-cortex lesion on learning hierarchically structured action sequences. Using a visual-manual serial reaction time task, we had subjects first perform five blocks of trials with a hierarchically structured 14-element action sequence and then tested for sequence-specific learning by introducing a pseudo-random transfer sequence. Relative to control subjects (N = 39), we found that both lateral frontal (N = 16) and medial frontal (N = 18) patients showed reduced overall performance benefits across the training phase. In contrast, the negative transfer test showed significantly increased reaction times in all patient groups, indicating robust sequence-specific learning. This learning was not significantly different from that of the control group. Taken together, the data suggest that learning hierarchically structured action sequences is unimpaired in patients with prefrontal-cortex lesion.

The Left Lateral cortex is known to have a role in inductive reasoning tasks. A more specific hypothesis on its role is that it is crucial in the generation of new abstract rules, rather than in the selection and implementation of a specific rule among a set of previously learned ones. Two new tests - the Generation of Hypotheses test and the Recognition of the Rule test - were administered to 46 patients with focal damage to the frontal cortex. Patients were divided in three frontal subgroups: Left Lateral, Right Lateral and Medial. On the basis of the new hypothesis, it was predicted that (i) the Left Lateral subgroup would fail in the Generation of Hypotheses test but would show spared performance on the Recognition of the Rule test and that (ii) the other frontal subgroups would perform normally on both tests. The findings on the Left Lateral and Right Lateral frontal subgroup were consistent with the predictions. This suggests that the Left Lateral frontal cortex is critical specifically for the generation of hypotheses in inductive reasoning. The Medial frontal subgroup, in contrast with our expectations, was impaired on Generation test; two hypotheses have been raised to explain this finding.

A recently proposed theory on frontal lobe functions claims that the prefrontal cortex, particularly its dorso-lateral aspect, is crucial in defining a set of responses suitable for a particular task, and biasing these for selection. This activity is carried out for virtually any kind of non-routine tasks, without distinction of content. The aim of this study is to test the prediction of Frith's 'sculpting the response space' hypothesis by means of an 'insight' problem-solving task, namely the matchstick arithmetic task. Starting from Knoblich et al.'s interpretation for the failure of healthy controls to solve the matchstick problem, and Frith's theory on the role of dorsolateral frontal cortex, we derived the counterintuitive prediction that patients with focal damage to the lateral frontal cortex should perform better than a group of healthy participants on this rather difficult task. We administered the matchstick task to 35 patients (aged 26-65 years) with a single focal brain lesion as determined by a CT or an MRI scan, and to 23 healthy participants (aged 34-62 years). The findings seemed in line with theoretical predictions. While only 43% of healthy participants could solve the most difficult matchstick problems ('type C'), 82% of lateral frontal patients did so (Fisher's exact test, P < 0.05). In conclusion, the combination of Frith's and Knoblich et al.'s theories was corroborated.

The neural correlates of inductive reasoning are still poorly understood. In order to explore them, we administered a revised version of the Brixton test, a rule attainment task, to a group of 40 patients with a focal frontal brain lesion of mixed aetiology and to 43 control subjects. To interpret an impairment on the test as suggesting an inductive reasoning deficit a number of alternative hypotheses need first to be considered, namely whether the Brixton impairment could be explained by: (i) a working memory deficit; (ii) a monitoring deficit; (iii) a difficulty in applying an already induced rule; (iv) greater impulsivity. The patients with left lateral (LL) frontal lesions were significantly impaired on the Brixton test; more importantly they were the only group in which none of the alternative hypotheses we explored proved able to explain the flawed performance. In sharp contrast, right lateral lesion patients did not make significantly more errors on the Brixton test than controls, but they produced three times more capture errors (a sign of impaired monitoring processes). The results were interpreted as suggesting functional dissociations between inductive reasoning, monitoring and working memory and a localisation of key processes for induction in left lateral frontal cortex and in right lateral cortex for monitoring and checking.

Per lo studio di alcuni compiti linguistici, come la produzione libera di parole di una certa categoria («fluenza semantica»), è necessario disporre di indici quantitativi (come la frequenza, la familiarità, ecc.) per tutti gli elementi della categoria in questione, in quanto non è possibile prevedere quali di essi saranno prodotti dal soggetto sperimentale. La stima preliminare di questi indici su soggetti normali è difficile nel caso di categorie semantiche molto ampie, o in cui siano frequentemente introdotti nuovi esemplari. Per questi motivi, la nostra scelta è caduta sulla categoria «frutta» per la quale presentiamo in questo lavoro i valori di alcune variabili semantico-lessicali raccolti su soggetti normali. La «frutta» è sembrata utile non solo perché ha un numero contenuto di esemplari, ma anche perché essa si articola in sottocategorie, e ciò è vantaggioso per alcuni modelli di applicazione clinica. L’inventario dei membri della categoria è stato fatto mediante un compito preliminare di fluenza semantica, che ha fornito nell’insieme dei soggetti esaminati un elenco di 84 frutti. Un diverso campione di soggetti ha stimato familiarità, prototipicità ed età di acquisizione di ciascuno degli 84 frutti, e la prossimità semantica tra ciascuna delle coppie formate dai 32 frutti più frequentemente prodotti. Sulla matrice di prossimità è stata eseguita una cluster analysis che ha messo in luce in quali sottogruppi la categoria «frutta» possa essere empiricamente suddivisa. Accanto ad una presentazione dei modelli principali del compito di fluenza semantica, si discutono ed esemplificano su due soggetti normali alcune possibili applicazioni cliniche destinate a soggetti cerebrolesi.

It has been suggested that neglect patients misrepresent the metric spatial relations along the horizontal axis (anisometry). The "fabric" of their internal spatial medium would be distorted in such a way that physically equal distances appear relatively shorter on the contralesional side (canonical anisometry). The case of GL, a 76-year-old lady with left neglect on visual search tasks, is presented. GL showed severe relative overestimation on the left (contralesional) side on two independent tasks evaluating the metrics of her internal representation. A qualitatively similar pattern was found in two out of 10 other neglect patients who performed the second task. This behavior cannot be accounted for by the canonical anisometry hypothesis. Nevertheless, GL produced a relative left overextension (underestimation) when trying to set the endpoints of a virtual line given its midpoint (Endpoints Task). An interpretation of these results is offered in terms of a misprojection of relevant landmarks onto the internal representation without assuming distortion of its "fabric."