Recruitment of the occipital cortex by arithmetic processing follows computational bias in the congenitally blind.

Arithmetic reasoning activates the occipital cortex of congenitally blind people (CB). This activation of visual areas may highlight the functional flexibility of occipital regions deprived of their dominant inputs or relate to the intrinsic computational role of specific occipital regions. We contrasted these competing hypotheses by characterizing the brain activity of CB and sighted participants while performing subtraction, multiplication and a control letter task. In both groups, subtraction selectively activated a bilateral dorsal network commonly activated during spatial processing. Multiplication triggered activity in temporal regions thought to participate in memory retrieval. No between-group difference was observed for the multiplication task whereas subtraction induced enhanced activity in the right dorsal occipital cortex of the blind individuals only. As this area overlaps with regions showing selective tuning to auditory spatial processing and exhibits increased functional connectivity with a dorsal "spatial" network, our results suggest that the recruitment of occipital regions during high-level cognition in the blind actually relates to the intrinsic computational role of the activated regions.

Detecting over-reporting of symptoms: the French version of the self-report symptom inventory.

OBJECTIVE: Symptom exaggeration and malingering are core issues in forensic and clinical evaluation. Generally, experts use two main types of instruments to assess the credibility of symptoms: performance validity tests that aim to detect underperformance and self-report validity tests that appraise over-reporting of symptoms. However, while many tools can be used to assess underperformance, far fewer instruments are available to evaluate over-reporting of symptoms. METHODS: In this study, we adapted the Self-Report Symptom Inventory (SRSI) for use with French-speaking participants and tested its psychometric properties on a sample of 575 healthy adults (aged from 18 to 65 years), alongside various smaller subgroups. RESULTS: Exploratory and confirmatory factor analyses supported a two-factor structure for the scale, with a first factor including items questioning genuine symptoms and a second factor including items questioning bizarre or rare symptoms (i.e., pseudosymptoms). Additional analyses emphasized the SRSI's excellent internal reliability and good convergent validity. Furthermore, our results revealed that both the symptom and pseudosymptom subscales were able to discriminate between participants who were asked to feign cognitive impairments (i.e., malingerers), healthy controls, and patients with genuine cognitive symptoms. CONCLUSION: Overall, these results suggest that the SRSI may be considered a promising tool to assess the credibility of symptoms in patients evaluated in forensic contexts.

How should proxies of cognitive reserve be evaluated in a population of healthy older adults?

BACKGROUND: While some tools have been developed to estimate an individual's cognitive reserve (CR), no study has assessed the adequacy of the method used for assessing these CR proxy indicators. Therefore, we aimed to determine the most appropriate method to estimate CR by comparing two approaches: (1) the common assessment of CR proxies in the literature (e.g. years of education) and (2) the calculation of a comprehensive index based on most significant parameters used in the estimation of CR. METHODS: Data on CR proxies (i.e. education, occupation, and leisure activities) were obtained in a sample of 204 older adults. Regression analyses were used to develop the two indices of CR (i.e. ICR-standard and ICR-detailed) and to determine which index best represented the level of one's CR. RESULTS: The ICR-standard was calculated using a combination of the three most common measures of reserve in the literature: number of schooling years, complexity of the primary occupation, and amount of current participation in stimulating activities. The ICR-detailed was calculated using the most significant parameters (established in initial analyses) of CR: highest level of education combined with the number of training courses, last occupation, and amount of current participation in social and intellectual activities. The comparison of both indices showed that higher levels of ICR-standard and ICR-detailed were associated with a greater minimization of the effects of age on cognition. However, the ICR-detailed was more strongly associated to this minimization than the ICR-standard, suggesting that the ICR-detailed best reflect one's CR. CONCLUSIONS: This study is the first to show that it is of great importance to question methods measuring CR proxies in order to develop a clinical tool allowing a comprehensive and accurate estimation of CR.

Visual experience influences the interactions between fingers and numbers.

Though a clear interaction between finger and number representations has been demonstrated, what drives the development of this intertwining remains unclear. Here we tested early blind, late blind and sighted control participants in two counting tasks, each performed under three different conditions: a resting condition, a condition requiring hands movements and a condition requiring feet movements. In the resting condition, every sighted and late blind spontaneously used their fingers, while the majority of early blind did not. Sighted controls and late blind were moreover selectively disrupted by the interfering hand condition, while the early blind who did not use the finger-counting strategy remained unaffected by the interference conditions. These results therefore demonstrate that visual experience plays an important role in implementing the sensori-motor habits that drive the development of finger-number interactions.

The processing of symbolic and nonsymbolic ratios in school-age children.

This study tested the processing of ratios of natural numbers in school-age children. Nine- and eleven-year-olds were presented collections made up of orange and grey dots (i.e., nonsymbolic format) and fractions (i.e., symbolic format). They were asked to estimate ratios between the number of orange dots and the total number of dots and fractions by producing an equivalent ratio of surface areas (filling up a virtual glass). First, we tested whether symbolic notation of ratios affects their processing by directly comparing performance on fractions with that on dot sets. Second, we investigated whether children's estimates of nonsymbolic ratios of natural numbers relied at least in part on ratios of surface areas by contrasting a condition in which the ratio of surface areas occupied by dots covaried with the ratio of natural numbers and a condition in which this ratio of surface areas was kept constant across ratios of natural numbers. The results showed that symbolic notation did not really have a negative impact on performance among 9-year-olds, while it led to more accurate estimates in 11-year-olds. Furthermore, in dot conditions, children's estimates increased consistently with ratios between the number of orange dots and the total number of dots even when the ratio of surface areas was kept constant but were less accurate in that condition than when the ratio of surface areas covaried with the ratio of natural numbers. In summary, these results indicate that mental magnitude representation is more accurate when it is activated from symbolic ratios in children as young as 11 years old and that school-age children rely at least in part on ratios of surface areas to process nonsymbolic ratios of natural numbers when given the opportunity to do so.

Embodied numbers: the role of vision in the development of number-space interactions.

The strong association between numbers and space is found in the well-documented SNARC effect (Spatial Numerical Association of Response Codes), where responses on small/large numbers are faster in the left/right side of space, respectively. However, little is known about the developmental process through which numbers are mapped onto external physical space. Here we show that early blind individuals, but not late blind or sighted, demonstrate a reversed SNARC effect when performing a numerical comparison task with hands crossed over the body midline. Importantly, this reversed SNARC effect was not observed in any group of participants in a control parity judgment task. The present study therefore demonstrates that early visual experience drives the development of an external coordinate system for the visuo-spatial representation of numbers and further supports the idea that different types of spatial information are engaged in specific numerical tasks.

Increased sensitivity to proactive and retroactive interference in amnestic mild cognitive impairment: new insights.

BACKGROUND: Increased sensitivity to proactive (PI) and retroactive (RI) interference has been observed in amnestic mild cognitive impairment (aMCI). PI and RI are often explained as being the result of a response competition mechanism. However, patients with aMCI are supposed to suffer mostly from encoding deficits. We hypothesized that in aMCI interference may occur at encoding and not only at the retrieval stage. MATERIAL AND METHODS: We developed an original paradigm enabling PI and RI to be tested with and without response competitors. Eighteen young controls (YC), 16 elderly controls (EC) and 15 aMCI participated in the study. RESULTS: The YC and EC groups presented interference effects only in conditions that included a direct response competitor. In contrast, aMCI had interference effects in all conditions including the one without response competitor. CONCLUSION: Increased sensitivity to interference in aMCI appears to occur at the encoding/consolidation stage and not only at the retrieval stage, as is the case in healthy subjects. This result is discussed in the context of the associative encoding deficits characterizing aMCI.

Over-estimation in numerosity estimation tasks: more than an attentional bias?

Over- and under-estimation have been observed in numerosity estimation and approximate arithmetic tasks. Two different models have been proposed to account for these reverse patterns of performance: 1) the bi-directional mapping account (Crollen, Castronovo, & Seron, 2011); 2) the operational momentum hypothesis (McCrink, Dehaene, & Dehaene-Lambertz, 2007). Our study was designed to examine whether the operational momentum could account for the over-estimation found in numerosity estimation tasks. To this aim, a series of 3 experiments involving a symbolic to non-symbolic numerical mapping and a rightward or leftward displacement along the mental number line were designed. Over-estimation was observed in these three tasks irrespective of the direction and size of the displacement to be done on the mental number line. These results thus clearly demonstrated that overestimation was not merely due to an attentional bias, but rather relied on the cognitive operation of mapping two differently scaled numerical representations.

Effect of cognitive load on working memory forgetting in aging.

Functional approaches to working memory (WM) have been proposed recently to better investigate "maintenance" and "processing" mechanisms. The cognitive load (CL) hypothesis presented in the "Time-Based Resource-Sharing" model (Barrouillet & Camos, 2007) suggests that forgetting from WM (maintenance) can be investigated by varying the presentation rate and processing speed (processing). In this study, young and elderly participants were compared on WM tasks in which the difference in processing speed was controlled by CL manipulations. Two main results were found. First, when time constraints (CL) were matched for the two groups, no aging effect was observed. Second, whereas a large variation in CL affected WM performance, a small CL manipulation had no effect on the elderly. This suggests that WM forgetting cannot be completely accounted for by the CL hypothesis. Rather, it highlights the need to explore restoration times in particular, and the nature of the refreshment mechanisms within maintenance.

The mental representation of the magnitude of symbolic and nonsymbolic ratios in adults.

This study mainly investigated the specificity of the processing of fraction magnitudes. Adults performed a magnitude-estimation task on fractions, the ratios of collections of dots, and the ratios of surface areas. Their performance on fractions was directly compared with that on nonsymbolic ratios. At odds with the hypothesis that the symbolic notation impedes the processing of the ratio magnitudes, the estimates were less variable and more accurate for fractions than for nonsymbolic ratios. This indicates that the symbolic notation activated a more precise mental representation than did the nonsymbolic ratios. This study also showed, for both fractions and the ratios of dot collections, that the larger the components the less precise the mental representation of the magnitude of the ratio. This effect suggests that the mental representation of the magnitude of the ratio was activated from the mental representation of the magnitude of the components and the processing of their numerical relation (indirect access). Finally, because most previous studies of fractions have used a numerical comparison task, we tested whether the mental representation of magnitude activated in the fraction-estimation task could also underlie performance in the fraction-comparison task. The subjective distance between the fractions to be compared was computed from the mean and the variability of the estimates. This distance was the best predictor of the time taken to compare the fractions, suggesting that the same approximate mental representation of the magnitude was activated in both tasks.

The role of vision in the development of finger-number interactions: Finger-counting and finger-montring in blind children.

Previous research has suggested that the use of the fingers may play a functional role in the development of a mature counting system. However, the role of developmental vision in the elaboration of a finger numeral representation remains unexplored. In the current study, 14 congenitally blind children and 14 matched sighted controls undertook three different test batteries that examined (a) general cognitive abilities, (b) the spontaneous use of finger-counting and finger-montring strategies (where "finger-montring" is a term used to characterize the way people raise their fingers to show numerosities to other people), and (c) the canonicity level of the finger-counting and finger-montring habits. Compared with sighted controls, blind children used their fingers less spontaneously to count and in a less canonical way to count and show quantities. These results demonstrate that the absence of vision precludes the development of a typical finger numeral representation and suggest that the use of canonical finger-counting and finger-montring strategies relies on the visual recognition of particular hand shapes.

Associative encoding deficits in amnestic mild cognitive impairment: a volumetric and functional MRI study.

BACKGROUND: Previous functional MRI studies have shown increased hippocampus activation in response to item encoding in amnestic mild cognitive impairment (aMCI). Recent behavioral studies suggested that associative memory could be more impaired than item memory in aMCI. So far, associative encoding has not been evaluated separately from item encoding in functional MRI studies. METHODS: We conducted a volumetric and functional MRI study investigating associative encoding in 16 aMCI and 16 elderly controls while controlling for item encoding. RESULTS: We confirmed the presence of associative memory impairment in aMCI even after controlling for item memory differences between groups. Associative memory but not item memory correlated with hippocampus volume in aMCI. Such a correlation was not observed in elderly controls. The left anterior hippocampus activation in response to successful associative encoding was decreased in aMCI, even after correction for hippocampus atrophy. CONCLUSION: Associative memory impairment in aMCI appears to be related to hippocampus atrophy and left anterior hippocampus hypoactivation.

Under- and over-estimation: a bi-directional mapping process between symbolic and non-symbolic representations of number?

Over the last 30 years, numerical estimation has been largely studied. Recently, Castronovo and Seron (2007) proposed the bi-directional mapping hypothesis in order to account for the finding that dependent on the type of estimation task (perception vs. production of numerosities), reverse patterns of performance are found (i.e., under- and over-estimation, respectively). Here, we further investigated this hypothesis by submitting adult participants to three types of numerical estimation task: (1) a perception task, in which participants had to estimate the numerosity of a non-symbolic collection; (2) a production task, in which participants had to approximately produce the numerosity of a symbolic numerical input; and (3) a reproduction task, in which participants had to reproduce the numerosity of a non-symbolic numerical input. Our results gave further support to the finding that different patterns of performance are found according to the type of estimation task: (1) under-estimation in the perception task; (2) over-estimation in the production task; and (3) accurate estimation in the reproduction task. Moreover, correlation analyses revealed that the more a participant under-estimated in the perception task, the more he/she over-estimated in the production task. We discussed these empirical data by showing how they can be accounted by the bi-directional mapping hypothesis (Castronovo & Seron, 2007).

Superior estimation abilities in two autistic spectrum children.

Anecdotal reports of superior estimation abilities in autistic individuals (e.g., Sacks, 1985) have never been confirmed empirically. We present here case studies of 2 children with autistic spectrum diagnoses and report remarkable abilities in estimation for several quantifiable dimensions. K.T. and G.T. were tested at 9 years of age for estimation of rank, numerosity, time, weight, length, surface, distance, and precise enumeration for small numbers. Their performances were compared to those of 6 age- and IQ- matched comparison children. K.T. demonstrated a superior level of performance in estimating rank (e.g., which set has larger numerosity?) but his performance in other tasks was average. G.T. displayed outstanding performance in estimating numerosity, time, weight, surface, length, and distance, with average performance in other tasks. These results show that certain autistic spectrum individuals may develop superior and highly specialized abilities in estimation. We discuss these findings in relation to the role of "veridical mapping" in the development of special ability (Mottron, Dawson, & Soulieres, 2009; Mottron, Dawson, Soulieres, Hubert, & Burack, 2006a). Veridical mapping is the detection of isomorphism within a code, between two codes, or between one code and isomorphic elements of the world. Within this framework, it is proposed that estimation abilities, like absolute pitch, rely on the ability to map a verbal code with a specific magnitude of a psychophysical dimension.

Increased sensitivity to proactive interference in amnestic mild cognitive impairment is independent of associative and semantic impairment.

Episodic memory deficit is the hallmark of amnestic mild cognitive impairment (aMCI). There is, however, an overlap in performance among patients with aMCI and elderly controls (EC). The memory deficit in aMCI therefore needs to be better characterized. Studies have shown that associative memory is selectively impaired in aMCI, and recent work suggested that aMCI may be hypersensitive to semantic proactive interference (PI). It is not known whether this increased PI is related to associative or semantic impairment. EC (n=44) and patients with aMCI (n=30) performed two tasks presenting a gradually increasing PI effect across four lists. One task used semantic cueing, the other phonological cueing. We controlled for associative memory by introducing it as a covariate and by matching our subjects for it. Patients with aMCI had a greater PI effect than EC matched for associative memory, regardless of the type of cueing. The increased PI effect in patients with aMCI is independent of their associative and semantic impairment.

Numerical estimation in blind subjects: evidence of the impact of blindness and its following experience.

Vision was for a long time considered to be essential in the elaboration of the semantic numerical representation. However, early visual deprivation does not seem to preclude the development of a spatial continuum oriented from left to right to represent numbers (J. Castronovo & X. Seron, 2007; D. Szücs & V. Csépe, 2005). The authors investigated the impact of blindness and its following experience on a 3rd property of the mental number line: its obedience to Weber's law. A group of blind subjects and a group of sighted subjects were submitted to 2 numerical estimation tasks: (a) a keypress estimation task and (b) an auditory events estimation task. Blind and sighted subjects' performance obeyed Weber's law. However, blind subjects demonstrated better numerical estimation abilities than did sighted subjects, especially in contexts involving proprioception, indicating the existence of better mapping abilities between the symbolic representations of numbers and their corresponding magnitude representations, obeying Weber's law (e.g., J. S. Lipton & E. Spelke, 2005). These findings suggest that blindness and its following experience with numbers might result in better accuracy in numerical processing.

Contribution of hand motor circuits to counting.

The finding that number processing activates a cortical network partly overlapping that recruited for hand movements has renewed interest in the relationship between number and finger representations. Further evidence about a possible link between fingers and numbers comes from developmental studies showing that finger movements play a crucial role in learning counting. However, increased activity in hand motor circuits during counting may unveil unspecific processes, such as shifting attention, reciting number names, or matching items with a number name. To address this issue, we used transcranial magnetic stimulation to measure changes in corticospinal (CS) excitability during a counting task performed silently and using either numbers or letters of the alphabet to enumerate items. We found an increased CS excitability of hand muscles during the counting task, irrespective of the use of numbers or letters, whereas it was unchanged in arm and foot muscles. Control tasks allowed us to rule out a possible influence of attention allocation or covert speech on CS excitability increase of hand muscles during counting. The present results support a specific involvement of hand motor circuits in counting because no CS changes were found in arm and foot muscles during the same task. However, the contribution of hand motor areas is not exclusively related to number processing because an increase in CS excitability was also found when letters were used to enumerate items. This finding suggests that hand motor circuits are involved whenever items have to be put in correspondence with the elements of any ordered series.

Semantic numerical representation in blind subjects: the role of vision in the spatial format of the mental number line.

Does vision play a role in the elaboration of the semantic representation of small and large numerosities, notably in its spatial format? To investigate this issue, we decided to compare in the auditory modality the performance of congenitally and early blind people with that of a sighted control group, in two number comparison tasks (to 5 and to 55) and in one parity judgement task. Blind and sighted participants presented exactly the same distance and SNARC (Spatial Numerical Association of Response Codes) effects, indicating that they share the same semantic numerical representation. In consequence, our results suggest that the spatial dimension of the numerical representation is not necessarily attributable to the visual modality and that the absence of vision does not preclude the elaboration of this representation for 1-digit (Experiment 1) and 2-digit numerosities (Experiment 2). Moreover, as classical semantic numerical effects were observed in the auditory modality, the postulate of the amodal nature of the mental number line for both small and large magnitudes was reinforced.

Finger-digit compatibility in Arabic numeral processing.

Finger-digit response compatibility was tested by asking participants to identify Arabic digits by pressing 1 of 10 keys with all 10 fingers. The direction of the finger-digit mapping was varied by manipulating the global direction of the hand-digit mapping as well as the direction of the finger-digit mapping within each hand (in each case, from small to large digits, or the reverse). The hypothesis of a left-to-right mental number line predicted that a complete left-to-right mapping should be easier whereas the hypothesis of a representation based on finger counting predicted that a counting-congruent mapping should be easier. The results show that when all 10 fingers are used to answer, a mapping congruent with the prototypical finger-counting strategy reported by the participants leads to better performance than does a mapping congruent with a left-to-right oriented mental number line, both in palm-down and palm-up postures of the hands, and they demonstrate that finger-counting strategies influence the way that numerical information is mentally represented and processed.