Behavioral and neuroimaging evidence for a contribution of color and texture information to scene classification in a patient with visual form agnosia

A common notion is that object perception is a necessary precursor to scene perception. Behavioral evidence suggests, however, that scene perception can operate independently of object perception. Further, neuroimaging has revealed a specialized human cortical area for viewing scenes that is anatomically distinct from areas activated by viewing objects. Here we show that an individual with visual form agnosia, D.F., who has a profound deficit in object recognition but spared color and visual texture perception, could still classify scenes and that she was fastest when the scenes were presented in the appropriate color. When scenes were presented as black-and-white images, she made a large number of errors in classification. Functional magnetic resonance imaging revealed selective activation in the parahippocampal place area (PPA) when D.F. viewed scenes. Unlike control observers, D.F. demonstrated higher activation in the PPA for scenes presented in the appropriate color than for black-and-white versions. The results demonstrate that an individual with profound form vision deficits can still use visual texture and color to classify scenes-and that this intact ability is reflected in differential activation of the PPA with colored versions of scenes.     

Equivalency of Spanish language versions of the trail making test part B including or excluding "CH"

Spanish speakers commonly use two versions of the alphabet, one that includes the sound "Ch" between C and D and another that goes directly to D, as in English. Versions of the Trail Making Test Part B (TMT-B) have been created accordingly to accommodate this preference. The pattern and total number of circles to be connected are identical between versions. However, the equivalency of these alternate forms has not been reported. We compared the performance of 35 healthy Spanish speakers who completed the "Ch" form (CH group) to that of 96 individuals who received the standard form (D group), based on whether they mentioned "Ch" in their oral recitation of the alphabet. The groups had comparable demographic characteristics and overall neuropsychological performance. There were no significant differences in TMT-B scores between the CH and D groups, and relationships with demographic variables were comparable. The findings suggest that both versions are equivalent and can be administered to Spanish speakers based on their preference without sacrificing comparability.     

Cognitive impairment of aphasics in a colour-to-picture matching task.

Broca's and Wernicke's aphasics, non-aphasic brain-damaged patients and chronic schizophrenics were tested in a colour-to-picture matching task. For each of 42 black-and-white drawings of objects the most "typical" colour was to be selected from a set of 24 colour strips. Separate scores for the appropriateness of the choices as to hue, brightness, and saturation were obtained by comparison with the data from 50 normal Ss. The choices of both aphasic groups were more deviant than those of brain-damaged controls for chromatically coloured objects with respect to all three colour dimensions, and for achromatically coloured objects with respect to saturation and brightness. Wherever the aphasics' performance was worse than that of the controls, the deviancy-scores correlated significantly with the Token Test. Results are interpreted as an impairment of aphasics in the ability to isolate analytically specific features of objects or concepts which might be conceived of as a prerequisite of propositional language.     

Recognition of visual stimuli and memory for spatial context in schizophrenic patients and healthy volunteers

Verbal and visual recognition tasks were administered to 40 patients with schizophrenia and 40 healthy comparison subjects. The verbal recognition task consisted of discriminating between 16 target words and 16 new words. The visual recognition task consisted of discriminating between 16 target pictures (8 black-and-white and 8 color) and 16 new pictures (8 black-and-white and 8 color). Visual recognition was followed by a spatial context discrimination task in which subjects were required to remember the spatial location of the target pictures at encoding. Results showed that recognition deficit in patients was similar for verbal and visual material. In both schizophrenic and healthy groups, men, but not women, obtained better recognition scores for the colored than for the black-and-white pictures. However, men and women similarly benefited from color to reduce spatial context discrimination errors. Patients showed a significant deficit in remembering the spatial location of the pictures, independently of accuracy in remembering the pictures themselves. These data suggest that patients are impaired in the amount of visual information that they can encode. With regards to the perceptual attributes of the stimuli, memory for spatial information appears to be affected, but not processing of color information.     

Learning and memory in streptozotocin-induced diabetic rats in a novel spatial/object discrimination task

Diabetes mellitus is associated with disturbances of cognitive functioning. The aim of this study was to examine cognitive functioning in diabetic rats using the 'Can test', a novel spatial/object learning and memory task, without the use of aversive stimuli. Rats were trained to select a single rewarded can from seven cans. Mild water deprivation provided the motivation to obtain the reward (0.3 ml of water). After 5 days of baseline training, in which the rewarded can was marked by its surface and position in an open field, the animals were divided into two groups. Diabetes was induced in one group, by an intravenous injection of streptozotocin. Retention of baseline training was tested at 2-weekly intervals for 10 weeks. Next, two adapted versions of the task were used, with 4 days of training in each version. The rewarded can was a soft-drink can with coloured print. In a 'simple visual task' the soft-drink can was placed among six white cans, whereas in a 'complex visual task' it was placed among six soft-drink cans from different brands with distinct prints. In diabetic rats the number of correct responses was lower and number of reference and working memory errors higher than in controls in the various versions of the test. Switches between tasks and increases in task complexity accentuated the performance deficits, which may reflect an inability of diabetic rats to adapt behavioural strategies to the demands of the tasks.     

Visual preferences of students with profound mental retardation and healthy,full-term infants

Thirty students with profound mental retardation (age range: 3-5 to 19-11) and 30 healthy, full-term infants (5-8 months) were shown 12 stimuli, three times each. Four patterned stimuli were presented one to a card and each pattern appeared in black-and-white, black-and-yellow, and red-and-yellow. Both groups looked significantly longer at face patterns than other patterns. Students with profound mental retardation looked longer at black-and-white patterns than other color combinations. Infants looked longer at red and yellow cards than did students with profound mental retardation. The measurement method was practical, reliable, and sensitive to both within and between group differences. Results from this assessment method may help determine the most salient visual stimuli for evoking active-alert states for students with profound mental retardation. Individual variability was evident in the data, which demonstrates the importance of examining preferences for each individual when planning intervention. Implications for future research and intervention are discussed.     

Distinct electrophysiological indices of maintenance in auditory and visual short-term memory

We compared the electrophysiological correlates for the maintenance of non-musical tones sequences in auditory short-term memory (ASTM) to those for the short-term maintenance of sequences of coloured disks held in visual short-term memory (VSTM). The visual stimuli yielded a sustained posterior contralateral negativity (SPCN), suggesting that the maintenance of sequences of coloured stimuli engaged structures similar to those involved in the maintenance of simultaneous visual displays. On the other hand, maintenance of acoustic sequences produced a sustained negativity at fronto-central sites. This component is named the Sustained Anterior Negativity (SAN). The amplitude of the SAN increased with increasing load in ASTM and predicted individual differences in the performance. There was no SAN in a control condition with the same auditory stimuli but no memory task, nor one associated with visual memory. These results suggest that the SAN is an index of brain activity related to the maintenance of representations in ASTM that is distinct from the maintenance of representations in VSTM.     

Development of the Texas Spanish Naming Test: A Test For Spanish Speakers

Neuropsychological assessment of Spanish speakers often involves translated versions of English measures, with limited validation data and potential bias due to cultural, educational, and linguistic differences. The Texas Spanish Naming Test (TNT), a 30-item confrontation naming test, was developed for Spanish speakers by systematically selecting culturally salient words. In a sample of 85 minimally educated Spanish speakers, the TNT demonstrated good internal consistency and convergent validity, and showed greater sensitivity than a translated version of the popular Boston Naming Test. Results support the clinical utility of the TNT when dementia among Spanish speakers is suspected.     

Development of the Texas Spanish Naming Test: a test for Spanish speakers

Neuropsychological assessment of Spanish speakers often involves translated versions of English measures, with limited validation data and potential bias due to cultural, educational, and linguistic differences. The Texas Spanish Naming Test (TNT), a 30-item confrontation naming test, was developed for Spanish speakers by systematically selecting culturally salient words. In a sample of 85 minimally educated Spanish speakers, the TNT demonstrated good internal consistency and convergent validity, and showed greater sensitivity than a translated version of the popular Boston Naming Test. Results support the clinical utility of the TNT when dementia among Spanish speakers is suspected.     

Evidence for hemispheric specialization of lexical distinctions in bilingual Chinese-Mandarin speakers

Lexical decision vocal reaction times of a group of English-proficient, Chinese-Mandarin speakers and group of monolingual, English speakers were measured to unilaterally presented concrete and abstract English words. Results of an ANOVA showed a significant group x visual field x stimulus type interaction. Post-hoc analysis showed a significant right visual field advantage for the Chinese subjects. For the English speaking subjects, right visual field stimulations yielded significantly faster vocal reaction times to the abstract words than to the concrete ones, while the opposite occurred for left visual-field inputs. Also, a correlation between the two lateral conditions was significant for the Chinese subjects but not for the English speakers. These findings suggest that the English speakers evidenced dissociated left and right hemispheric linguistic processing while the Chinese subjects left hemisphere was responsible for the final phonological stages of linguistic analysis. Such findings support a phonological "monitor-user" hypothesis for cerebral dominance characteristics in bilingual Chinese speakers.     

Colour knowledge in semantic dementia: it is not all black and white

In three experiments we assessed the colour knowledge of patients with semantic dementia, a neuro-degenerative condition that gradually erodes conceptual knowledge. In Experiment 1, the patients’ colour naming performance correlated strongly with their object naming for frequency-matched items, with no patient showing better-than-expected naming of colours relative to objects. In Experiment 2, where patients were asked to colour black-and-white line drawings of common objects, all patients were impaired relative to controls, and performance correlated strongly with degree of semantic deficit. The fact that patients often erroneously selected green for fruits or vegetables, and brown for animals, suggests some preservation of general knowledge about the colours that typify a given domain. In Experiment 3, patients were given pairs of identical line drawings of familiar animals, fruits and vegetables—one of each pair coloured correctly, and one incorrectly—and were asked to choose the correct one. When the target's colour was characteristic of the domain, patients scored well; but when the distractor had a typical hue and the target's colour was unusual (e.g. a green versus an orange carrot), performance was far poorer. The results are discussed with reference to alternative theories about the neural basis of conceptual knowledge.     

Detecting gradual visual changes in colour and brightness agnosia: a double dissociation

Two patients, one with colour agnosia and one with brightness agnosia, performed a task that required the detection of gradual temporal changes in colour and brightness. The results for these patients, who showed anaverage or an above-average performance on several tasks designed to test low-level colour and luminance (contrast) perception in the spatial domain, yielded a double dissociation; the brightness agnosic patient was within the normal range for the coloured stimuli, but much slower to detect brightness differences, whereas the colour agnosic patient was within the normal range for the achromatic stimuli, but much slower for the coloured stimuli. These results suggest that a modality-specific impairment in the detection of gradual temporal changes might be related to, if not underlie, the phenomenon of visual agnosia.     

Colour recognition at large visual eccentricities in normal observers and patients with low vision

When we look at our spatial environment we have the feeling that the whole visual field is coloured, yet the density of cone photoreceptors decreases considerably as eccentricity increases. We investigated colour perception (coloured/noncoloured), colour naming and whether colour helps object recognition at eccentricities varying from 0 degrees to 80 degrees in healthy observers and patients with low vision. We found that colours can be perceived and even identified above chance at very large eccentricities (60 degrees). When asked to categorize coloured and grey level objects as edible/nonedible, both healthy observers and patients with low vision showed better performance for coloured edible objects at 50 degrees suggesting that colour is used for object recognition in conditions of degraded form perception.     

Comparison of different statistical analyses in visual stimulus fMRI

The present study evaluated four different clinically relevant statistical approaches with respect to a response to a visual stimulus paradigm. Healthy volunteers were subjected to a visual stimulus consisting of a checkerboard black-and-white box car pattern with on-off blocks of 10s. Simultaneously, sensitivity encoding (SENSE) dynamic MR imaging was acquired using a 1.5 T MR system. Statistical analyses were conducted with z-cluster analysis, Student's t-test, Spearman's correlation, and time-series normalized cross-correlation. A figure-of-merit for neural activity was measured from calculated maps using pixel counting. The results demonstrated that the index of activity estimated from the number of "activated" pixels did not differ markedly among the four different statistical methods, except when comparing the cross-correlation statistics with z-clustering in the whole brain, implying that all methods lead to similar statistical information when using fMRI to map the activity of the visual cortex in response to a visual stimulus.     

Interaction of frontal and perirhinal cortices in visual object recognition memory in monkeys

Monkeys were trained preoperatively in visual object recognition memory. The task was delayed matching‐to‐sample with lists of trial‐unique randomly generated visual stimuli in an automated apparatus, and the stimuli were 2D visual objects made from randomly generated coloured shapes. We then examined the effect of either: (i) disconnecting the frontal cortex in one hemisphere from the perirhinal cortex in the contralateral hemisphere by crossed unilateral ablations; (ii) disconnecting the magnocellular portion of the mediodorsal (MDmc) thalamic nucleus in one hemisphere from the perirhinal cortex in the contralateral hemisphere; or (iii) bilaterally ablating first the amygdala, then adding fornix transection, then finally perirhinal cortex ablation. We found that both frontal/perirhinal and MDmc/perirhinal disconnection had a large effect on visual object recognition memory, whereas both amygdalectomy and the addition of fornix transection had only a mild effect. We conclude that the frontal lobe needs to interact with the perirhinal cortex within the same hemisphere for visual object recognition memory, but that routes through the amygdala and hippocampus are not of primary importance.     

Early involvement of the temporal area in attentional selection of grating orientation: an ERP study

The aim of the present study was to investigate the neural mechanisms of stimulus orientation selection in humans by recording event-related potentials (ERPs) of the brain with a 32-channel montage. Stimuli were isoluminant black-and-white gratings (3 cpd) having an orientation of 50, 70, 90, 110 and 130, randomly presented in the foveal portion (2 of visual angle) of the central visual field. The task consisted in selectively attending and responding to one of the five grating orientations, while ignoring the others. ERP results showed that orientation selection affected neural processing starting already at an early post-stimulus latency. The P1 component (80-140 ms) measured at temporal area, which might well be reflecting the activity of the ventral stream (i.e. 'WHAT' system) of the visual pathways, showed an enhanced amplitude for target orientations. These effects increased with progressive neural processing over time as reflected by selection negativity (SN) and P300 components. In addition, both reaction times (RTs) and ERPs showed a strong 'oblique' effect, very probably reflecting the perceptual predominance of orthogonal versus oblique stimulus orientation in the human visual system: RTs were much faster, and SN and P300 components much larger, to gratings presented vertically than in other orientations.     

Inconstant nonverbal recognition memory in Korsakoff patients and controls

Eleven alcoholic Korsakoff patients, 12 alcoholic controls, and 12 volunteers were asked to remember complex nonverbal items (8 bird calls and 8 coloured geometric art patterns) across each of 3 auditory and 3 visual tests of recurrent recognition. Item-by-item analyses of correct recognitions indicated that Korsakoff patients forgot many items, yet recovered other to-be-remembered items from one test to the next. Influenced by decision uncertainty, the recognition memory of Korsakoff patients (as estimated in measures derived from Signal Detection Theory) declined across tests in the auditory task, that of chronic alcoholics only in the visual task. Neither the item fluctuation nor the low decision criteria adopted by Korsakoff patients were found to be task-specific.     

Auditory perceptual evaluation of rhythm-manipulated and resynthesized sentence utterances obtained from cerebellar patients and normal speakers: A preliminary report

Alterations of the temporal structure of spoken utterances in terms of lengthened acoustic segments and increased syllabic isochrony seem to represent a salient feature of ataxic dysarthria. The present study addresses the question of whether systematic manipulations of the durational aspects of the acoustic speech signal yield an improvement of perceived dysarthric deficits. Different variants of speech rhythm were imposed on sentence utterances obtained from two patients with ataxic dysarthria and two normal control speakers. For the sake of comparability the pitch contours were standardized by means of linearly interpolated stylized versions. The introduced manipulations significantly influenced the ratings of perceived slowness, dysfluency, and rhythmic adequacy. With respect to estimates of overall intelligibility and naturalness, however, ataxic-dysarthric utterances did not benefit from any synthetic changes. By contrast, utterances of normal speakers were rated less intelligible and somewhat more unnatural when resynthesized with an ataxic rhythm. These results indicate that durational factors play a minor role with respect to the overall speech impairment of ataxic speakers.