Focusing and orienting spatial attention differently modulate crowding in central and peripheral vision

The allocation of attentional resources to a particular location or object in space involves two distinct processes: an orienting process and a focusing process. Indeed, it has been demonstrated that performance of different visual tasks can be improved when a cue, such as a dot, anticipates the position of the target (orienting), or when its dimensions (as in the case of a small square) inform about the size of the attentional window (focusing). Here, we examine the role of these two components of visuo-spatial attention (orienting and focusing) in modulating crowding in peripheral (Experiment 1 and Experiment 3a) and foveal (Experiment 2 and Experiment 3b) vision. The task required to discriminate the orientation of a target letter "T,'' close to acuity threshold, presented with left and right "H'' flankers, as a function of target-flanker distance. Three cue types have been used: a red dot, a small square, and a big square. In peripheral vision (Experiment 1 and Experiment 3a), we found a significant improvement with the red dot and no advantage when a small square was used as a cue. In central vision (Experiment 2 and Experiment 3b), only the small square significantly improved participants' performance, reducing the critical distance needed to recover target identification. Taken together, the results indicate a behavioral dissociation of orienting and focusing attention in their capability of modulating crowding. In particular, we confirmed that orientation of attention can modulate crowding in visual periphery, while we found that focal attention can modulate foveal crowdin

Agnosic vision is like peripheral vision, which is limited by crowding

Abstract Visual agnosia is a neuropsychological impairment of visual object recognition despite near-normal acuity and visual fields. A century of research has provided only a rudimentary account of the functional damage underlying this deficit. We find that the object-recognition ability of agnosic patients viewing an object directly is like that of normally-sighted observers viewing it indirectly, with peripheral vision. Thus, agnosic vision is like peripheral vision. We obtained 14 visual-object-recognition tests that are commonly used for diagnosis of visual agnosia. Our "standard" normal observer took these tests at various eccentricities in his periphery. Analyzing the published data of 32 apperceptive agnosia patients and a group of 14 posterior cortical atrophy (PCA) patients on these tests, we find that each patient's pattern of object recognition deficits is well characterized by one number, the equivalent eccentricity at which our standard observer's peripheral vision is like the central vision of the agnosic patient. In other words, each agnosic patient's equivalent eccentricity is conserved across tests. Across patients, equivalent eccentricity ranges from 4 to 40 deg, which rates severity of the visual deficit. In normal peripheral vision, the required size to perceive a simple image (e.g., an isolated letter) is limited by acuity, and that for a complex image (e.g., a face or a word) is limited by crowding. In crowding, adjacent simple objects appear unrecognizably jumbled unless their spacing exceeds the crowding distance, which grows linearly with eccentricity. Besides conservation of equivalent eccentricity across object-recognition tests, we also find conservation, from eccentricity to agnosia, of the relative susceptibility of recognition of ten visual tests. These findings show that agnosic vision is like eccentric vision. Whence crowding? Peripheral vision, strabismic amblyopia, and possibly apperceptive agnosia are all limited by crowding, making it urgent to know what drives crowding. Acuity does not (Song et al., 2014), but neural density might: neurons per deg2 in the crowding-relevant cortical area

Perceptualand cognitive factors imposing "speed limits" on reading rate: a study with the rapid serial visual presentation

Adults read at high speed, but estimates of their reading rate vary greatly, i.e., from 100 to 1500 words per minute (wpm). This discrepancy is likely due to different recording methods and to the different perceptual and cognitive processes involved in specific test conditions. The present study investigated the origins of these notable differences in RSVP reading rate (RR). In six experiments we investigated the role of many different perceptual and cognitive variables. The presence of a mask caused a steep decline in reading rate, with an estimated masking cost of about 200 wpm. When the decoding process was isolated, RR approached values of 1200 wpm. When the number of stimuli exceeded the short-term memory span, RR decreased to 800 wpm. The semantic context contributed to reading speed only by a factor of 1.4. Finally, eye movements imposed an upper limit on RR (around 300 wpm). Overall, data indicate a speed limit of 300 wpm, which corresponds to the time needed for eye movement execution, i.e., the most time consuming mechanism. Results reconcile differences in reading rates reported by different laboratories and thus provide suggestions for targeting different components of reading rate

Decision times in orthographic processing: a cross-linguistic study

Reading comparisons across transparent and opaque orthographies indicate critical differences that may reveal the mechanisms involved in orthographic decoding across orthographies. Here, we address the role of criterion and speed of processing in accounting for performance differences across languages. We used binary tasks involving orthographic (words–pseudowords), and non-orthographic materials (female–male faces), and analyzed results based on Ratcliff’s Diffusion model. In the first study, 29 English and 28 Italian university students were given a lexical decision test. English observers made more errors than Italian observers while showing generally similar reaction times. In terms of the diffusion model, the two groups differed in the decision criterion: English observers used a lower criterion. There was no overall cross-linguistic difference in processing speed, but English observers showed lower values for words (and a smaller lexicality effect) than Italians. In the second study, participants were given a face gender judgment test. Female faces were identified slower than the male ones with no language group differences. In terms of the diffusion model, there was no difference between groups in drift rate and boundary separation. Overall, the new main finding concerns a difference in decision criterion limited to the orthographic task: English individuals showed a more lenient criterion in judging the lexicality of the items, a tendency that may explain why, despite lower accuracy, they were not slower. It is concluded that binary tasks (and the Diffusion model) can reveal cross-linguistic differences in orthographic processing which would otherwise be difficult to detect in standard single-word reading tasks

Ability to Consolidate Instances as a Proxy for the Association Among Reading, Spelling, and Math Learning Skill

Learning skills (as well as disorders) tend to be associated; however, cognitive models typically focus either on reading, spelling or maths providing no clear basis for interpreting this phenomenon. A recent new model of learning cognitive skills proposes that the association among learning skills (and potentially the comorbidity of learning disorders) depends in part from the individual ability to consolidate instances (taken as a measure of rate of learning). We examined the performance of typically developing fifth graders over the acquisition of a novel paper-and-pencil task that could be solved based on an algorithm or, with practice, with reference to specific instances. Our aim was to establish a measure of individual rate of learning using parameters envisaged by the instance theory of automatization by Logan and correlate it to tasks requiring knowledge of individual items (e.g., spelling words with an ambiguous transcription) or tasks requiring the application of a rule or an algorithm (e.g., spelling non-words). The paper-and-pencil procedure yielded acquisition curves consistent with the predictions of the instance theory of automatization (i.e., they followed a power function fit) both at a group and an individual level. Performance in tasks requiring knowledge of individual items (such as doing tables or the retrieval of lexical representations) but not in tasks requiring the application of rules or algorithms (such as judging numerosity or spelling through sublexical mapping) was significantly predicted by the learning parameters of the individual power fits. The results support the hypothesis that an individual dimension of “ability to consolidate instances” contributes to learning skills such as reading, spelling, and maths, providing an interesting heuristic for understanding the comorbidity across learning disorders

Dissociation in optokinetic stimulation sensitivity between omission and substitution reading errors in neglect dyslexia

Although omission and substitution errors in neglect dyslexia (ND) patients have always been considered as different manifestations of the same acquired reading disorder, recently, we proposed a new dual mechanism model. While omissions are related to the exploratory disorder which characterizes unilateral spatial neglect (USN), substitutions are due to a perceptual integration mechanism. A consequence of this hypothesis is that spe- cific training for omission-type ND patients would aim at restoring the oculo-motor scanning and should not improve reading in substitution-type ND. With this aim we administered an optokinetic stimulation (OKS) to two brain-damaged patients with both USN and ND, MA and EP, who showed ND mainly characterized by omissions and substitutions, respectively. MA also showed an impairment in oculo-motor behavior with a non-reading task, while EP did not. The two patients presented a dissociation with respect to their sensitivity to OKS, so that, as expected, MA was positively affected, while EP was not. Our results confirm a dissociation between the two mechanisms underlying omission and substitution reading errors in ND patients. Moreover, they suggest that such a dissociation could possibly be extended to the effectiveness of rehabilitative procedures, and that patients who mainly omit contralesional-sided letters would benefit from OKS

Population pharmacokinetics and probability of target attainment of meropenem in critically ill patients

Purpose: Patients admitted to intensive care unit (ICU) with Klebsiella pneumoniae infections are characterized by high mortality. The aims of the present study were to investigate the population pharmacokinetics parameters and to assess the probability of target attainment of meropenem in critically ill patients to provide information for more effective regimens. Methods: Twenty-seven consecutive patients were included in the study. Meropenem was administered as 3-h intravenous (i.v.) infusions at doses of 1\u20132 g every 8 or 12 h. Meropenem plasma concentrations were measured by a high-performance liquid chromatography (HPLC) method, and a population pharmacokinetics analysis was performed using NONMEM software. Meropenem plasma disposition was simulated for extended (3 h; 5 h) or continuous i.v. infusions, and the following parameters were calculated: time during which free drug concentrations were above minimum inhibitory concentration (MIC) (fT > MIC), free minimum plasma concentrations above 4 7 MIC (fCmin > 4 7 MIC), probability of target attainment (PTA), and cumulative fraction of response (CFR). Results: Gender and severity of sepsis affected meropenem clearance, whose typical population values ranged from 6.22 up to 12.04 L/h (mean \ub1 standard deviation (SD) value, 9.38 \ub1 4.47 L/h). Mean Cmin value was 7.90 \ub1 7.91 mg/L, suggesting a high interindividual variability. The simulation confirmed that 88 and 97.5 % of patients achieved effective Cmin > 4 7 MIC values after 3- and 5-h i.v. infusions of meropenem 2 g  7 3/day, respectively. On the contrary, the same total daily doses reached the target Cmin > 4 7 MIC values in 100 % of patients when administered as continuous i.v. infusions. Conclusions: Several factors may influence meropenem pharmacokinetics in ICU patients. Continuous i.v. infusions of meropenem seem to be more effective than standard regimens to achieve optimal therapeutic targets

How accurate is an LCD screen version of the Pelli–Robson test?

Purpose: To evaluate the accuracy and repeatability of a computer-generated Pelli–Robson test displayed on liquid crystal display (LCD) systems compared to a standard Pelli–Robson chart. Methods: Two different randomized crossover experiments were carried out for two different LCD systems for 32 subjects: 6 females and 10 males (40.5 ± 13.0 years) and 9 females and 7 males (27.8 ± 12.2 years), respectively, in the first and second experiment. Two repeated measurements were taken with the printed Pelli–Robson test and with the LCDs at 1 and 3 m. To test LCD reliability, measurements were repeated after 1 week. Results: In Experiment 1, contrast sensitivity (CS) measured with LCD1 resulted significantly higher than Pelli–Robson both at 1 and at 3 m of about 0.20 log 1/C in both eyes (p < 0.01). Bland–Altman plots showed a proportional bias for LCD1 measures. LCD1 measurements showed reasonable repeatability: ICC was 0.83 and 0.65 at 1 and 3 m, respectively. In Experiment 2, CS measured with LCD2 resulted significantly lower than Pelli–Robson both at 1 and at 3 m of about 0.10 log 1/C in both eyes (p < 0.01). Bland–Altman plots did not show any proportional bias for LCD2 measures. LCD2 measurements showed sufficient repeatability: ICC resulted 0.51 and 0.65 at 1 and 3 m, respectively. Conclusions: Computer-generated versions of Pelli–Robson test, displayed on LCD systems, do not provide accurate results compared to classic Pelli–Robson printed version. Clinicians should consider that Pelli–Robson computer-generated versions could be non-interchangeable to the printed version

Inconstancy and inconsistency of visual illusory phenomena? The case of the Poggendorff Figure

Since its conception the Poggendorff Figure has always been studied by considering the absolute role of the variables involved in determining the illusion (e.g. the angle or the distance between the inducer and the test stimuli). By contrast, we suggest that the role of such variables is relative to the specific conditions in which the illusory configuration is presented; in particular, we propose that multiple variables enter the computation leading to the Poggendorff Illusion, but that their relative weight varies as a function of the specific experimental conditions adopted. Here, we measured the point of subjective collinearity between the oblique lines of the Poggendorff Figure as a function of the orientation of the inducer (a square), the orientation of the test stimuli (changing the linear distance between them) and the size of the whole configuration. We found that when the inducer square was upright the illusory effect varied according to the distance between the test segments, while when the square was tilted the effect was determined only by its orientation. Critically, the latter condition led to a reversal of the ‘classic’ illusory effect. Leveling the playing field in terms of the information available to the observer, the results indicate that the illusory effect is determined by different types of processing in different conditions of stimulus presentation