Simona Gardini

Stimulus‐driven attentional capture: An empirical comparison of display‐size and distance methods

Four experiments examined attentional capture by colour as assessed by two different investigative methods. Subjects performed a visual search task for a vertical-target line embedded among tilted-distractor lines, presented inside 4, 8, or 12 coloured discs. Interestingly, when the colour singleton was task irrelevant, and data were analysed by means of the display-size method combined with the zero-slope criterion, no evidence for attentional capture by colour was found. However, when data were analysed by means of the distance method, which consists of monitoring the spatial relationship between the target and the singleton, results showed that the target was found faster and/or more accurately when it was inside the singleton than when it was in a nonsingleton location. This provided evidence for a stimulus-driven attentional capture. In addition, the application of signal detection methodology showed that attentional capture, as revealed by the distance method, resulted from a perceptual modulation at the singleton location, rather than from a criterion shift. We conclude that, at least with the kind of stimuli used here, the display-size method combined with the zero-slope criterion is less than ideal for investigating how static discontinuities can affect the automatic deployment of visual attention.

The generation and maintenance of visual mental images: Evidence from image type and aging

Imagery is a multi-componential process involving different mental operations. This paper addresses whether separate processes underlie the generation, maintenance and transformation of mental images or whether these cognitive processes rely on the same mental functions. We also examine the influence of age on these mental operations for independence of components. In Experiment 1, younger (22 years) and older (69 years) adults generated and maintained general, specific, contextual and autobiographical visual mental images evoked in response to concrete nouns. The older adults had longer generation times, but there was no difference between the two groups on maintenance. Both groups had shortest generation and maintenance times for general images, whereas only the older adults took longest in generating autobiographical images. In Experiment 2, the total maintenance time and number of transformations for each type of image were compared in another group of younger and older adults. General images were less transformed and more subject to decay for both groups. The older people maintained the autobiographical mental images for longest compared to other image types. In conclusion, image generation, maintenance and transformation seem to be differently affected by type of image and aging, supporting a model of their cognitive segregation.

Different neuronal pathways support the generation of general and specific mental images.

The aim of this functional magnetic resonance imaging (fMRI) study was to investigate the neural correlates associated with the generation of general (i.e., prototypical) and specific (i.e., exemplar) visual mental images from concrete nouns. The fMRI paradigm included a non-imagery baseline, and two activation conditions requiring the generation of either general or specific images. Image generation times and brain activation were recorded. Analysis of the behavioral results showed that generating general images took less than the specific ones. The comparison of each activation condition with the baseline showed significant increase in brain activation in left frontal areas in both kinds of images, with the additional involvement of the posterior cingulate cortex during the generation of specific images. When the two activation conditions were contrasted with each other and masked for their respective comparison with baseline, significant activation was found in right frontal areas for general mental images, whereas a significant increase in activation in the left superior frontal region and the right thalamus was detected during the generation of specific mental images. These findings suggest that general and specific mental images are generated with the support of two different neural pathways. The generation of general images seems to involve brain areas associated with the formation of global gestalt-like images (areas in the right hemisphere), while the generation of specific mental images appears to require additional support from areas involved in the retrieval of visual details (i.e., the right thalamus).

Increased Functional Connectivity in the Default Mode Network in Mild Cognitive Impairment: A Maladaptive Compensatory Mechanism Associated with Poor Semantic Memory Performance

Semantic memory decline and changes of default mode network (DMN) connectivity have been reported in mild cognitive impairment (MCI). Only a few studies, however, have investigated the role of changes of activity in the DMN on semantic memory in this clinical condition. The present study aimed to investigate more extensively the relationship between semantic memory impairment and DMN intrinsic connectivity in MCI. Twenty-one MCI patients and 21 healthy elderly controls matched for demographic variables took part in this study. All participants underwent a comprehensive semantic battery including tasks of category fluency, visual naming and naming from definition for objects, actions and famous people, word-association for early and late acquired words and reading. A subgroup of the original sample (16 MCI patients and 20 healthy elderly controls) was also scanned with resting state functional magnetic resonance imaging and DMN connectivity was estimated using a seed-based approach. Compared with healthy elderly, patients showed an extensive semantic memory decline in category fluency, visual naming, naming from definition, words-association, and reading tasks. Patients presented increased DMN connectivity between the medial prefrontal regions and the posterior cingulate and between the posterior cingulate and the parahippocampus and anterior hippocampus. MCI patients also showed a significant negative correlation of medial prefrontal gyrus connectivity with parahippocampus and posterior hippocampus and visual naming performance. Our findings suggest that increasing DMN connectivity may contribute to semantic memory deficits in MCI, specifically in visual naming. Increased DMN connectivity with posterior cingulate and medio-temporal regions seems to represent a maladaptive reorganization of brain functions in MCI, which detrimentally contributes to cognitive impairment in this clinical population.

Reduced grey matter in the posterior insula as a structural vulnerability or diathesis to addiction

A number of neuroimaging studies have shown that drug addiction is associated with morphological differences in several brain areas, including orbito-frontal and limbic structures. Most of these studies have investigated patients with addiction to cocaine. The neurobiological mechanisms which play a role in drug addiction are not fully understood, however, and the causal factors remain under investigation. The present study investigated morphological differences between patients with history of cocaine (N=14) and heroin (N=24) abuse and healthy matched controls (N=24). A 3D T1W MRI scan was acquired for all participants and the grey matter images of each patient group compared with those of controls. A direct comparison of the two addiction groups was also carried out. When compared with controls cocaine dependent patients had lower grey matter values in the left middle occipital gyrus, right putamen and insula, whereas heroin abusers had lower grey matter values in the right insula. The direct comparison between the two addiction groups showed that cocaine abusers had less grey matter in the right posterior cingulate, medio-temporal and cerebellar regions, whereas heroin abusers showed less grey matter in parietal regions on both sides, including postcentral gyrus and inferior parietal lobule. Reduced right posterior insular cortex was commonly found in both cocaine and heroin dependent patients. This morphological difference might represent a structural marker of addiction, which is independent of the discrete regional effects of each psychotropic substance of abuse, and might constitute a possible neurobiological vulnerability or diathesis to addiction. Equally, the discrete structural differences emerging from the direct comparison of cocaine and heroin abusers might reflect the effects of differential drug binding in the brain and/or express a form of neurobiological vulnerability which might explain individual drug choice.

Visuo-spatial imagery impairment in posterior cortical atrophy: a cognitive and SPECT study.

This study investigated the cognitive profile and the cerebral perfusion pattern in a highly educated 70 year old gentleman with posterior cortical atrophy (PCA). Visuo-perceptual abilities, spatial memory, spatial representation and navigation, visuo-spatial mental imagery, semantic and episodic-autobiographical memory were assessed. Regional cerebral blood flow (rCBF) was imaged with SPECT. Cognitive testing showed visual-perceptual impairment, apperceptive visual and landmark agnosia, topographical disorientation with way-finding deficits, impaired map learning and poor mental image generation. Semantic memory was normal, while episodic-autobiographical memory was impaired. Reduced rCBF was found mainly in the right hemisphere, in the precentral gyrus, posterior cingulate and middle temporal gyri, cuneus and precuneus, in the left superior temporal and lingual gyri and in the parahippocampus bilaterally. Hypoperfusion in occipito-parietal regions was associated with visuo-spatial deficits, whereas deficits in visuo-spatial mental imagery might reflect dysfunction related to hypoperfusion in the parahippocampus and precuneus, structures which are responsible for spatial and imagery processing. Dissociating performance between preserved semantic memory and poor episodic-autobiographical recall is consistent with a pattern of normal perfusion in frontal and anterior temporal regions but abnormal rCBF in the parahippocampi. The present findings indicate that PCA involves visuo-spatial imagery deficits and provide further validation to current neuro-cognitive models of spatial representation and topographical disorientation.

Cognitive and neuronal processes involved in sequential generation of general and specific mental images

Mental image generation is a complex process mediated by dynamically interrelated components, e.g. image generation and image enrichment of details. This study investigated the cognitive and neural correlates of sequential image generation. An event-related fMRI experiment was carried out in which general and specific images had to be generated sequentially in two different positions. Participants had to generate either a general image first and then a specific one or a specific image first and then a general one, in response to the same word-stimulus. Generation times showed that specific images took shorter to be produced if they had been preceded by the generation of a general image. The fMRI results showed that position of generation and type of image was associated with different patterns of neurofunctional change. When an image was generated as first, areas of activation were found in the parahippocampal, fusiform and occipital regions. These are areas associated with memory retrieval and visual processing. When an image was generated as second, significant activations were found in superior temporal and precuneus areas, brain structures that are involved in the storage of visual memory for object shapes and imagery, respectively. The generation of a general image was supported by frontal areas and by the precuneus. The generation of a specific image involved frontal and thalamic areas (structures associated with visual processing of details) and the posterior cingulate cortex. When shifting from a specific image to a general one, a higher level of activity was found in the middle frontal gyrus involved in global visuo-spatial processing, suggesting that the generation of specific images required the retrieval of an object’s global shape. Altogether, these data suggest that the sequential generation of different types of image is associated with discrete processes but also shares common cognitive and neural components.

Italian norms for the Freedman version of the Clock Drawing Test

Background: The Clock Drawing Test (CDT) is a valid screening tool for the evaluation of cognitive decline. This study aimed to compute standardized norms for the Freedman version of the CDT in a population of 248 healthy Italian individuals aged from 20 to 89 years. Method: The effects of age, education, and gender on performance were assessed. Three conditions were administered: free-drawn clock (FD), which required participants to draw the contour, numbers, hands, and center of the clock; predrawn clock (PD), in which numbers, hands, and center had to be included in a predrawn contour; examiner-drawn clock (ED), in which only hands and center had to be inserted in a template including a predrawn contour and numbers. Scores for each of the single conditions and a total score were calculated. Results: Age had no effect on the FD condition, whereas a significant effect of age was found for the PD and ED conditions and the total score. Gender and education had no influence on any of the scores. Correction grids, cutoffs, and equivalent scores were computed. Conclusion: Standardized norms for the Freedman version of the CDT were collected in a large sample of healthy individuals. No adjustments were required for scores on the free-drawn condition, whereas raw scores on the predrawn and examiner-drawn conditions and the total score needed adjustments to account for age effects. The availability of standardized norms for this version of the CDT could increase the use of this comprehensive tool in the detection of dementia.

Brain Structural Substrates of Semantic Memory Decline in Mild Cognitive Impairment

Semantic memory decline has been found in mild cognitive impairment (MCI). In this study performance on a range of semantic tasks and structural brain patterns were examined in a group of MCI patients. Fourteen MCI and sixteen healthy elderly controls underwent semantic memory assessment and MRI brain scanning. The cognitive battery included visual naming and naming from definition tasks for objects, actions and famous people, semantic fluency for animals, fruits, tools, furniture, singers, politicians, actions, word-association task for early and late acquired words and a reading task. MCI patients performed worse on semantic fluency in all categories except for tools, produced a smaller number of words associated with early acquired nouns and a smaller total number of word-associations. Patients scored more poorly in all tasks of naming, naming of famous people, overall reading and reading of famous peoples names. MCIs had fewer correct immediate recalls and more correct responses with cue in famous people naming, made more errors in naming and in the naming from definition task for famous people. Grey matter reduction in parahippocampus, frontal and cingulate cortices and amygdala was found in the MCI sample when compared with controls. Patients presented a different pattern of brain areas correlated with semantic tasks from that seen in controls, with more extensive involvement of subcortical regions in semantic fluency and word-association and more contribution of frontal than temporo-parietal areas in visual naming. This evidence suggests a reorganization of cortical associations of semantic processes in MCI that, following damage in the semantic circuit, explains its progressive breakdown.

Relationship between spatial ability, visuospatial working memory and self-assessed spatial orientation ability: a study in older adults

This paper describes some novel spatial tasks and questionnaires designed to assess spatial and orientation abilities. The new tasks and questionnaires were administered to a sample of 90 older adults (41 males, age range 57–90), along with some other tests of spatial ability (Minnesota Paper Form Board, Mental Rotations Test, and Embedded Figures Test) and tests of visuospatial working memory (Corsi’s Block Test and Visual Pattern Test). The internal reliability of the new tasks and questionnaires was analyzed, as well as their relationship with the spatial and working memory tests. The results showed that the new spatial tasks are reliable, correlate with working memory and spatial ability tests and, compared with the latters, show stronger correlations with the self-report questionnaires referring to orientation abilities. A model was also tested (with reference to Allen et al. in Intelligence 22:327–355, 1996) in which the new tasks were assumed to relate to spatial ability and predict orientation abilities as assessed by the self-report measures.