The temporal features of visual processing were compared between young and elderly healthy partic... more The temporal features of visual processing were compared between young and elderly healthy participants in visual object and word recognition tasks using the technique of random temporal sampling. The target stimuli were additively combined with a white noise field and were exposed very briefly (200 ms). Target visibility oscillated randomly throughout exposure duration by manipulating the signal-to-noise ratio (SNR). Classification images (CIs) based on response accuracy were calculated to reflect processing efficiency according to the time elapsed since target onset and the power of SNR oscillations in the 5-55 Hz range. CIs differed substantially across groups whereas individuals of the same group largely shared crucial features such that a machine learning algorithm reached 100% accuracy in classifying the data patterns of individual participants into their proper group. These findings demonstrate altered perceptual oscillations in healthy aging and are consistent with previous investigations showing brain oscillation anomalies in the elderly.
This study examined the temporal profile of spatial frequency processing in a word reading task i... more This study examined the temporal profile of spatial frequency processing in a word reading task in 16 normal adult readers. They had to report the word presented in a 200 ms display using a four-alternative forced-choice task (4AFC). The stimuli were made of an additive combination of the signal (i.e. the target word) and of a visual white noise patch wherein the signal-to-noise ratio varied randomly across stimulus duration. Four spatial frequency conditions were defined for the signal component of the stimulus (bandpass Butterworth filters with center frequencies of 1.2, 2.4, 4.8 and 9.6 cycles per degree). In contrast to the coarse-to-fine theory of visual recognition, the results show that the highest spatial frequency range dominates early processing, with a shift toward lower spatial frequencies at later points during stimulus exposure. This pattern interacted in a complex way with the temporal frequency content of signal-to-noise oscillations. The outcome of individual data p...
The shape identification performance of a patient with category-specific agnosia for biological o... more The shape identification performance of a patient with category-specific agnosia for biological objects (E.L.M.) was investigated. E.L.M.'s ability to remember the association between visual shapes and computer-screen locations was assessed. All shape sets comprised exemplars that differed along a single diagnostic dimension. Two shape sets shared values on nondiagnostic dimensions, whereas a third set had differences on a redundant second dimension. E.L.M. significantly benefited from information contained in the redundant second dimension indicating that he can extract object information concerning multiple visual dimensions. We propose that E.L.M.'s problem involves disambiguating exemplars that are closely located in multidimensional shape space.
Extent and limits of covert lexical activation in letter-by-letter reading
Neurocase, Aug 1, 2000
... Martin Arguin is chercheur-boursier of the Fonds de la Recherche en Santé du Québec. ... Simi... more ... Martin Arguin is chercheur-boursier of the Fonds de la Recherche en Santé du Québec. ... Similar demon-strations were also reported by Coslett and Saffran (1989) and by Coslett, Saffran, Green-baum, and Schwartz (1993). ...
The temporal profile of visual encoding in the recognition of familiar objects
Journal of Vision, Sep 6, 2019
Pure alexia: attempted rehabilitation and its implications for interpretation of the deficit
Neurocase, Jun 1, 1995
On the basis of data indicating the failure to encode letters as abstract orthographic identities... more On the basis of data indicating the failure to encode letters as abstract orthographic identities in a pure alexic patient (D.M.) coupled with hypotheses about the effect of such a failure on word reading, an attempt at changing the nature of letter processing in D.M. was conducted. The training procedures failed to produce any fundamental change in the operations used by D.M. to encode isolated letters or words. However, rapid and massive benefits occurred in the overall speed of reading as a result of the training program. These appear to result from an increased rate of letter identification and the faster integration of individual letters into letter combinations. The observations gathered throughout this rehabilitation attempt provided evidence which constrains the range of possible explanations for the characteristic features of pure alexia. It is proposed that the letter-by-letter reading procedure which is the hallmark of the disorder may follow from an incapacity to directly encode visual letters as abstract orthographic types.
Implicit lexical access in letter-by-letter reading is not mediated by the right hemisphere
Brain and Cognition, 1996
Can the N2pc ERP component track visual attention?
The cost of shifting tasks across consecutive trials was examined as a function of the time inter... more The cost of shifting tasks across consecutive trials was examined as a function of the time interval between a task-cue and a subsequent target (cue-to-target interval, CTI). Task-shift costs are assumed to index a process by which subjects reconfigure their task-set when they must perform different tasks across consecutive trials. In neurologically intact teenagers, increased CTI causes reduced task-shift costs since subjects have more time to reconfigure their task-set prior to target onset. Some closed head injury adolescents however, show no reduction of task-shift costs with increased CTI. This indicates that subjects are incapable of reconfiguring their task-set from the cue alone, they also require the target before they are able to initiate this reconfiguration.
Background: The perception of visual forms is crucial for effective interactions with our environ... more Background: The perception of visual forms is crucial for effective interactions with our environment and for the recognition of visual objects. Thus, to determine the codes underlying this function is a fundamental theoretical objective in the study of the visual forms perception. The vast majority of research in the field is based on a hypothetico-deductive approach. Thus, we first begin by formulating a theory, then we make predictions and finally we conduct experimental tests. After decades of application of this approach, the field remains far from having a consensus as to the traits underlying the representation of visual form. Our goal is to determine, without theoretical a priori or any bias whatsoever, the information underlying the discrimination and recognition of 3D visual forms in normal human adults. Methods: To this end, the adaptive bubble technique developed by Wang et al. [2011] is applied on six 3D synthetic objects under varying views from one test to another. This technique is based on the presentation of stimuli that are partially revealed through Gaussian windows, the location of which is random and the number of which is established in such a way as to maintain an established performance criterion. Gradually, the experimental program uses participants' performance to determine the stimulus regions that participants use to recognize objects. The synthetic objects used in this study are unfamiliar and were generated from a program produced at C. Edward Connor's lab, Johns Hopkins University School of Medicine. Results: The results were integrated across participants to establish regions of presented stimuli that determine the observers' ability to recognize them-i.e., diagnostic attributes. The results will be reported in graphical form with a Z scores mapping that will be superimposed on silhouettes of the objects presented during the experiment. This mapping makes it possible to quantify the importance of the different regions on the visible surface of an object for its recognition by the participants. Conclusions: The diagnostic attributes that have been identified are the best described in terms of surface fragments. Some of these fragments are located on or near the outer edge of the stimulus while others are relatively distant. The overlap is minimal between the effective attributes for the different points of view of the same object. This suggests that the traits underlying the recognition of objects are specific to the point of view. In other words, they do not generalize through the points of view.
The contribution of stereopsis in human visual shape perception was examined using stimuli with e... more The contribution of stereopsis in human visual shape perception was examined using stimuli with either null, normal, or reversed binocular disparity in an old/new object recognition task. The highest levels of recognition performance were observed with null and normal binocular disparity displays, which did not differ. However, reversed disparity led to significantly worse performance than either of the other display conditions. This indicates that stereopsis provides a continuous input to the mechanisms involved in shape perception.
One of two memory systems can be used to navigate in a new environment. Hippocampusdependent spat... more One of two memory systems can be used to navigate in a new environment. Hippocampusdependent spatial strategy consists of creating a cognitive map of an environment and caudate nucleus-dependent response strategy consists of memorizing a rigid sequence of turns. Spontaneous use of the response strategy is associated with greater activity and grey matter within the caudate nucleus while the spatial strategy is associated with greater activity and grey matter in the hippocampus. The caudate nucleus is involved in executive functions such as working memory, cognitive control and certain aspects of attention such as attentional disengaging. This study therefore aimed to investigate whether response learners would display better performance on tests of executive and attention functioning compared to spatial learners. Fifty participants completed the 4/8 virtual maze to assess navigational strategy, the forward and backward visual digit span and the Attention Network Test-Revised to assess both attention disengagement and cognitive control. Results revealed that response learners showed significantly higher working memory capacity, more efficient attention disengagement and better cognitive control. Results suggest that response learners, who putatively display more grey matter and activity in the caudate nucleus, are associated with better working memory span, cognitive control and attentional disengagement.
Four visual search experiments are reported which used simple 2D shapes varying on the global dim... more Four visual search experiments are reported which used simple 2D shapes varying on the global dimensions of aspect ratio/curvature or aspect ratio/tapering. Results indicate serial self-terminating search in all conditions. Most importantly, search rates are markedly modulated by the particular forms of structural relations existing between the targets and their distractors. Thus, single-feature targets with shape properties that are linearly separable from those of their distractors yield markedly faster search rates than linearly separable targets made of a conjunction of distractor features. In addition, linearly separable single-feature targets are searched at a much faster rate than single-feature targets which are not linearly separable. Follow-up experiments demonstrate that these conjunction and linear non-separability effects cannot be attributed to pairwise target-distractor discriminability differences across conditions. The main conclusions are that the shapes used are parsed according to elementary features in visual encoding, and that a linear discrimination mechanism is available which permits fast visual search rates if a single-feature target is linearly separable from its distractors.
An important characteristic of the word superiority effect (WSE) observed in normal subjects is t... more An important characteristic of the word superiority effect (WSE) observed in normal subjects is that it extends to words displayed in mixed case letters, e.g., fAdE is better identified than gAdE (McClelland, 1976). Because upper and lower case letters are treated as functionally equivalent within the orthographic system (e.g., "A"/"a" map onto abstract letter identities; Coltheart, 1981), it is often argued that orthographic codes mediate the WSE. In the present paper, we report an intact WSE in a letter-by-letter surface alexic (IH) when words and "wordlike" pseudowords were displayed quickly and then masked. Consistent with the claim that orthographic codes mediated these effects, the WSE extended to words typed in mixed case letters, and IH failed to show a WSE for the same class of words for which he has impaired orthographic knowledge; namely, low frequency words. Based on these results, we argue that IH gains better access to orthographic knowled...
Canadian Journal on Aging / La Revue canadienne du vieillissement, 2020
Cognistat is a cognitive screening test that is widely used in English-speaking countries. Its Fr... more Cognistat is a cognitive screening test that is widely used in English-speaking countries. Its French adaptation is now available. The present study aims to establish norms for a population aged 60 and over. One hundred and fifty-one participants aged between 60 and 84 years old with normal cognitive function were divided into 5 five-year age groups. The results on Cognistat are reported for each subtest and age group. Age has a significant effect in only two subtests (Attention and Language Comprehension), which suggests a reduced performance for older participants. However, these effects are very weak and irregular. For this reason and given data distribution, norms are proposed to define performance thresholds for the 15th (lower limit of the normal range), 10th (mild cognitive impairment) and 5th (clinically significant) percentiles for each subtest for the clinical use of Cognistat with individuals 60 years of age and older.
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Papers by Martin Arguin