Passive and active processes in visuo-spatial memory: double dissociation in developmental learning disabilities

The distinction between passive and active visuo-spatial memory has been useful to interpret various pattern of deficits reported in individual differences studies. However, this interpretation raises the issue of task difficulty, since active tasks could be failed simply because more complex and the corresponding deficit could reflect a reduced capacity of the system. We describe two children with Nonverbal Learning Disability whose performance provides evidence of a dissociation between passive and active memory processes. One of the children showed a selective impairment in passive tasks and performed flawlessly in active tasks, whereas the second child displayed the opposite pattern. These data suggest that a qualitative difference between passive and active processes does exist and that differences in performance do not reflect a lower/higher level of task difficulty. Further, these data underlie the importance of formulating theoretical models of visuo-spatial memory including both material-related (i.e., visual vs spatial) and process-related (i.e., passive vs active) distinctions.     

Arithmetic difficulties in children with visuospatial learning disability (VLD).

Eighteen children with visuospatial learning disability (VLD) were compared to normal control children on a series of numerical and calculation tasks. Oral and written (dictated) calculation was assessed and operations differed not only in terms of the type of number processing requirements but also in terms of their visuospatial demand. The aim was to disentangle errors due to visuospatial processing failure from those deriving from incorrect knowledge of calculation procedures. Results showed that all children had relatively good knowledge of numerical facts and there was no statistical difference between the groups. No group difference was found in the overall performance in oral calculation, but a significant difference was present when the children were required to complete the operations in writing, with the VLD group achieving poorer performance than the controls. Furthermore, VLD children had greater difficulties when operations required borrowing or carrying; this was particularly problematic in subtractions. The results indicate that VLD children do not have a generalised problem with calculation per se or number manipulation in general. Rather their problems concern dealing with some processes that govern calculation especially those loading on visuospatial abilities.     

Suggested visual hallucination without hypnosis enhances activity in visual areas of the brain

This functional Magnetic Resonance Imaging (fMRI) study investigated high and low suggestible people responding to two visual hallucination suggestions with and without a hypnotic induction. Participants in the study were asked to see color while looking at a grey image, and to see shades of grey while looking at a color image. High suggestible participants reported successful alterations in color perception in both tasks, both in and out of hypnosis, and showed a small benefit if hypnosis was induced. Low suggestible people could not perform the tasks successfully with or without the hypnotic induction. The fMRI results supported the self report data, and changes in brain activity were found in a number of visual areas. The results indicate that a hypnotic induction, although having the potential to enhance the ability of high suggestible people, is not necessary for the effective alteration of color perception by suggestion.     

Do seductive details do their damage in the context of graph comprehension? Insights from eye movements

In educational research, interesting but irrelevant materials are often considered seductive details, which are suspected to have detrimental effects on learning. Although seductive details have been mostly examined in the context of text comprehension, such elements are also used in graphs (e.g., depicting data points). In the present experiment, we investigated both seductive text and seductive pictures in the context of graph comprehension as well as the interaction of seductive details with spatial working memory capacity (SWMC). We recorded N = 68 students' eye movements, while they analyzed bar graphs in a within‐subject design. Data were analyzed with linear mixed‐effects models. Results show that seductive details did not affect students' graph reading performance but prolonged the task processing time. Eye‐fixation measures revealed that additional processing time was best explained by attention distraction towards the seductive material. SWMC did not affect the presence or the extent of the seductive details effect.     

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.     

Hypnotic induction decreases anterior default mode activity

The ‘default mode’ network refers to cortical areas that are active in the absence of goal-directed activity. In previous studies, decreased activity in the ‘default mode’ has always been associated with increased activation in task-relevant areas. We show that the induction of hypnosis can reduce anterior default mode activity during rest without increasing activity in other cortical regions. We assessed brain activation patterns of high and low suggestible people while resting in the fMRI scanner and while engaged in visual tasks, in and out of hypnosis. High suggestible participants in hypnosis showed decreased brain activity in the anterior parts of the default mode circuit. In low suggestible people, hypnotic induction produced no detectable changes in these regions, but instead deactivated areas involved in alertness. The findings indicate that hypnotic induction creates a distinctive and unique pattern of brain activation in highly suggestible subjects.     

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.     

Bisection of shapes and lines: analysis of the visual and motor aspects of pseudoneglect

This study examined the visual and motor components of pseudoneglect as expressed on horizontal bisection tasks. Ten participants were tested on bisection of lines and elliptical shapes and judgement of pretransected lines. Results showed the same magnitude of leftward error on all three tasks, in contrast to previous findings for patients with visuospatial neglect who are known to bisect ellipses and circles much more accurately than lines. Participants' mean line bisection error was significantly further to the left than the mean subjective midpoint found on the judgement task. The findings contradict the claim that the visual component of pseudoneglect is caused by the same mechanism that causes visuospatial neglect but support the hypothesis that the motor component of pseudoneglect is similar to directional hypometria.