Attention-referenced visual representations: evidence from impaired visual localization

Endogenous spatial attention directed to intracutaneous electrical stimuli on the forearms involves an external reference frame

In the present study, we examined whether the direction of attention while anticipating intracutaneous electrical stimuli on the left or right forearm occurs within an internal somatotopic or an external body-based reference frame. Participants placed their hands on a table in front of them in a normal position or in a crossed-hands position. A symbolic cue with a validity of 80% instructed participants to attend to either the left or the right side, which varied from trial to trial. Crossing the hands induces a conflict of internal and external reference frames which allows to determine the dominating reference frame(s). Analyses of the electroencephalogram (EEG) during the orienting phase revealed that crossing the arms did not induce a reversal of neural activity over central sites as a late direction attention-related positivity and increased ipsilateral alpha power over occipital and central sites was observed in both conditions. Hand position influenced the processing of the electrical stimuli as no effect of cue validity was observed on the P3a component in the crossed-hands position. Our results indicate that endogenous spatial attention to intracutaneous electrical stimuli primarily occurs within an external reference frame.

Cortical signatures of dyslexia and remediation: an intrinsic functional connectivity approach

This observational, cross-sectional study investigates cortical signatures of developmental dyslexia, particularly from the perspective of behavioral remediation. We employed resting-state fMRI, and compared intrinsic functional connectivity (iFC) patterns of known reading regions (seeds) among three dyslexia groups characterized by (a) no remediation (current reading and spelling deficits), (b) partial remediation (only reading deficit remediated), and (c) full remediation (both reading and spelling deficits remediated), and a group of age- and IQ-matched typically developing children (TDC) (total N = 44, age range = 7-15 years). We observed significant group differences in iFC of two seeds located in the left posterior reading network - left intraparietal sulcus (L.IPS) and left fusiform gyrus (L.FFG). Specifically, iFC between L.IPS and left middle frontal gyrus was significantly weaker in all dyslexia groups, irrespective of remediation status/literacy competence, suggesting that persistent dysfunction in the fronto-parietal attention network characterizes dyslexia. Additionally, relative to both TDC and the no remediation group, the remediation groups exhibited stronger iFC between L.FFG and right middle occipital gyrus (R.MOG). The full remediation group also exhibited stronger negative iFC between the same L.FFG seed and right medial prefrontal cortex (R.MPFC), a core region of the default network These results suggest that behavioral remediation may be associated with compensatory changes anchored in L.FFG, which reflect atypically stronger coupling between posterior visual regions (L.FFG-R.MOG) and greater functional segregation between task-positive and task-negative regions (L.FFG-R.MPFC). These findings were bolstered by significant relationships between the strength of the identified functional connections and literacy scores. We conclude that examining iFC can reveal cortical signatures of dyslexia with particular promise for monitoring neural changes associated with behavioral remediation.

Inhibition within a reference frame during the interpretation of spatial language

Spatial terms such as right are potentially ambiguous because they can refer to different regions of space when defined by competing reference frames (e.g., my right within a relative reference frame versus an object's right within an intrinsic reference frame). In such situations, previous research has suggested that multiple reference frames are initially activated, followed by inhibition of the reference frame that is not ultimately selected to define the spatial term. Reference frames are complex multi-component representations, raising the question of exactly which components of the non-selected frame are inhibited. It is possible that the whole frame may be inhibited, including all axes and endpoints, or that only select endpoints and axes may be inhibited. Three experiments conducted using a negative priming paradigm revealed that only certain components of the non-selected reference frame were inhibited, consistent with the idea that some axes are privileged. These results also suggest that the components of a reference frame can be independently accessed. Implications for representing and accessing spatial information are discussed.

Representing orientation: A coordinate-system hypothesis and evidence from developmental deficits

This article concerns how the orientations of objects are represented in the human brain. We propose a coordinate-system hypothesis of orientation representation (COR) and show that the hypothesis provides an explicit basis for interpreting orientation errors. Next, we report results from three studies of individuals with developmental deficits in the processing of orientation information, demonstrating that the COR hypothesis can interpret the error patterns in each study. We conclude by discussing several issues concerning the interpretation of our results, the COR hypothesis, and the use of developmental deficits as a basis for inferences about normal cognition.

Spatial representations and multiple-visual-systems hypotheses: evidence from a developmental deficit in visual location and orientation processing

AH, a young, well-educated woman, has a developmental deficit in processing visual location and orientation information. Her deficit manifests itself in a wide range of visual tasks, including visually-guided reaching, copying pictures and words, and responding verbally to the location or orientation of visual stimuli; however, her performance in non-visual localization tasks is intact. AH's visual location and orientation errors are systematic left-right or up-down reflections (e.g., reaching to the far right for an object on the far left). More specifically, the errors involve reflection across the point where AH's attention is focused, regardless of where her eyes are fixated. These results imply that at some level(s) of the visual system, locations and orientations of visual stimuli are represented in a spatial coordinate system with an origin defined by the focus of attention. In these attention-centered representations location is specified in terms of distance and direction of displacement from the attentional focus along horizontal and vertical reference axes. AH's errors, I argue, result from misrepresentation of displacement direction (e.g., left rather than right, down rather than up) along a reference axis. Several visual variables dramatically affected AH's performance in visual location and orientation tasks: She was much more accurate for stimuli that were brief, moving, flickering, low in contrast, or high in eccentricity, than for those that were long in duration, stationary, continuous, high in contrast, and low in eccentricity. These results suggest that location and orientation are computed in each of two visual subsystems, which I call transient and sustained, and that AH's deficit affects only the sustained subsystem. I argue that AH's performance poses challenges to multiple-visual-subsystems hypotheses proposed by Ungerleider and Mishkin (1982) and by Milner and Goodale (1995).

Updating space during imagined self- and array translations

Previous work has demonstrated superior spatial updating performance during imagined viewer rotation versus imagined object/array rotation. Studies have also suggested that rotations are more difficult to process than translations. In three studies, we examined whether the advantage seen for updating during imagined self-rotations would generalize to translations. The participants updated the positions of objects in a line extending either to the front and back of the viewer or to the right and left after imagining viewer or array translation. Experiments 1 and 2 replicated the effects seen in imagined rotation tasks. A response time and accuracy advantage was found for imagined viewer translation versus imagined array translation. In Experiment 3, we directly compared real and imagined self- and array translations and demonstrated an advantage for real versus imagined array translation. The results suggest that the advantage for imagined viewer transformations is not a function of the specific transformation, but rather of the ability to imagine and predict the outcome of a moving frame of reference.