Tool use moves the peri-personal space from the hand to the tip of the tool.

In this study, we used a visual target detection task to investigate three hypotheses about how the peri-personal space is extended after tool-use training: Addition, Extension, and Projection hypotheses. We compared the target detection performance before and after tool-use training. In both conditions, the participants held a hockey stick-like tool in their hands during the detection task. Furthermore, we added the no-tool-holding condition to the experimental design. In the no-tool-holding condition, a peri-hand space advantage in the visual target detection task was observed. When the participants held the tool with their hands, this peri-hand space advantage was lost. Furthermore, there was no peri-tool space advantage before tool training. After tool training, the peri-tool space advantage was observed. However, after tool training, the advantage of the peri-hand space was not observed. This result suggested that the peri-hand advantage was reduced by simply holding the tool because the participants lost the functionality of their hands. Furthermore, tool-use training improved detection performance only in the peri-tool space. Thus, these results supported the projection hypothesis that the peri-personal space advantage would move from the body to the functional part of the tool.

The Ebbinghaus illusion with small inducers appears larger on the right side.

The effects of left and right alignment on the Ebbinghaus illusion were investigated in three experiments. In Experiment 1, the Ebbinghaus illusion was presented on the left or right side, and the points of subjective equality (PSE) were measured. Only the central disk of the figure with small inducers was perceived larger when it was positioned on the right side rather than on the left. In Experiments 2 and 3, left, right, and central placement were used to determine if the results of Experiment 1 were caused by a decrease of the illusion on the left side or an increase of the illusion on the right side. There was no difference in the illusion effect between the left and the center; however, the illusion effect increased when the figure was presented on the right side. These results suggest that a hemispheric asymmetry for global and local spatial attention influences the laterality of the Ebbinghaus illusion.

Categorical and coordinate processing in object recognition depends on different spatial frequencies.

Previous studies have suggested that processing categorical spatial relations requires high spatial frequency (HSF) information, while coordinate spatial relations require low spatial frequency (LSF) information. The aim of the present study was to determine whether spatial frequency influences categorical and coordinate processing in object recognition. Participants performed two object-matching tasks for novel, non-nameable objects consisting of "geons" (c.f. Brain Cogn 71:181-186, 2009). For each original stimulus, categorical and coordinate transformations were applied to create comparison stimuli. These stimuli were high-pass/low-cut-filtered or low-pass/high-cut-filtered by a filter with a 2D Gaussian envelope. The categorical task consisted of the original and categorical-transformed objects. The coordinate task consisted of the original and coordinate-transformed objects. The non-filtered object image was presented on a CRT monitor, followed by a comparison object (non-filtered, high-pass-filtered, and low-pass-filtered stimuli). The results showed that the removal of HSF information from the object image produced longer reaction times (RTs) in the categorical task, while removal of LSF information produced longer RTs in the coordinate task. These results support spatial frequency processing theory, specifically Kosslyn's hypothesis and the double filtering frequency model.

Effects of the global and local attention on the processing of categorical and coordinate spatial relations.

Participants made categorical or coordinate spatial judgments on the global or local elements of shapes. Stimuli were composed of a horizontal line and two dots. In the Categorical task, participants judged whether the line was above or below the dots. In the Coordinate task, they judged whether the line would fit between the dots. Stimuli were made hierarchical so that the global patterns composed of a "global line" made of local dots-and-line units, and "global dot" made of a single dots-and-line unit. The results indicated that the categorical task was better performed when participants attended to the local level of the hierarchical stimuli. On the other hand, the coordinate task was better performed when they attended to the global level. These findings are consistent with computer simulation models of the attentional modulation of neuronal receptive fields' size suggesting that (1) coordinate spatial relations are more efficiently encoded when one attends to a relatively large region of space, whereas (2) categorical spatial relations are more efficiently encoded when one attends to a relatively small region of space.

Iconic memory and parietofrontal network: fMRI study using temporal integration.

We investigated the neural basis of iconic memory using functional magnetic resonance imaging. The parietofrontal network of selective attention is reportedly relevant to readout from iconic memory. We adopted a temporal integration task that requires iconic memory but not selective attention. The results showed that the task activated the parietofrontal network, confirming that the network is involved in readout from iconic memory. We further tested a condition in which temporal integration was performed by visual short-term memory but not by iconic memory. However, no brain region revealed higher activation for temporal integration by iconic memory than for temporal integration by visual short-term memory. This result suggested that there is no localized brain region specialized for iconic memory per se.

Parietal and frontal object areas underlie perception of object orientation in depth.

Recent studies have shown that the human parietal and frontal cortices are involved in object image perception. We hypothesized that the parietal/frontal object areas play a role in differentiating the orientations (i.e., views) of an object. By using functional magnetic resonance imaging, we compared brain activations while human observers differentiated between two object images in depth-orientation (orientation task) and activations while they differentiated the images in object identity (identity task). The left intraparietal area, right angular gyrus, and right inferior frontal areas were activated more for the orientation task than for the identity task. The occipitotemporal object areas, however, were activated equally for the two tasks. No region showed greater activation for the identity task. These results suggested that the parietal/frontal object areas encode view-dependent visual features and underlie object orientation perception.

Processing spatial relations with different apertures of attention.

Neuropsychological studies suggest the existence of lateralized networks that represent categorical and coordinate types of spatial information. In addition, studies with neural networks have shown that they encode more effectively categorical spatial judgments or coordinate spatial judgments, if their input is based, respectively, on units with relatively small, nonoverlapping receptive fields, as opposed to units with relatively large, overlapping receptive fields. These findings leave open the question of whether interactive processes between spatial detectors and types of spatial relations can be modulated by spatial attention. We hypothesized that spreading the attention window to encompass an area that includes two objects promotes coordinate spatial relations, based on coarse coding by large, overlapping, receptive fields. In contrast, narrowing attention to encompass an area that includes only one of the objects benefits categorical spatial relations, by effectively parsing space. By use of a cueing procedure, the spatial attention window was manipulated to select regions of differing areas. As predicted, when the attention window was large, coordinate spatial transformations were noticed faster than categorical transformations; in contrast, when the attention window was relatively smaller, categorical spatial transformations were noticed faster than coordinate transformations. Another novel finding was that coordinate changes were noticed faster when cueing an area that included both objects as well as the empty space between them than when simultaneously cueing both areas including the objects while leaving the gap between them uncued.

Exogenous attention differentially modulates the processing of categorical and coordinate spatial relations.

Carrasco and her colleagues have suggested that exogenous attention reduces the size of receptive fields at an attended location (Gobell & Carrasco, 2005; Yeshurun & Carrasco, 1998, 2000). Based on the hypothesis that categorical and coordinate spatial relations are more efficiently processed by smaller and larger receptive fields, respectively, we predicted that exogenous attention would be more beneficial to the processing of categorical spatial relations than coordinate spatial relations while it would disrupt the processing of coordinate spatial relations. To test these hypotheses, participants were tested using a variant of Posner's (1980) attentional cueing paradigm. Exogenous attention produced larger facilitative effects on categorical spatial processing than on coordinate spatial processing at a short cue-target stimulus onset asynchrony (100 ms, Experiment 1, N=28), and this result was replicated regardless of cue size in Experiment 2 (N=24). When the coordinate judgment was sufficiently difficult, exogenous attention disrupted the processing of coordinate spatial relations (Experiment 3, N=28). These findings indicate that exogenous attention can differentially modulate the processing of categorical and coordinate spatial relations.

Lateralized effects of categorical and coordinate spatial processing of component parts on the recognition of 3D non-nameable objects.

Participants performed two object-matching tasks for novel, non-nameable objects consisting of geons. For each original stimulus, two transformations were applied to create comparison stimuli. In the categorical transformation, a geon connected to geon A was moved to geon B. In the coordinate transformation, a geon connected to geon A was moved to a different position on geon A. The Categorical task consisted of the original and the categorically transformed objects. The Coordinate task consisted of the original and the coordinately transformed objects. The original object was presented to the central visual field, followed by a comparison object presented to the right or left visual half-fields (RVF and LVF). The results showed an RVF advantage for the Categorical task and an LVF advantage for the Coordinate task. The possibility that categorical and coordinate spatial processing subsystems would be basic computational elements for between- and within-category object recognition was discussed.

Hemispheric processing of categorical/metric properties in object recognition.

Participants indicated whether two sequentially presented objects were of the same category (between-task) or were identical (within-task). Functional magnetic resonance imaging was used to examine cortical activation during the tasks. During the between-task, the left inferior parietal lobule was more activated than the right. During the within-task, the right superior occipital gyrus was more activated than the left. These results suggest that a hemispheric asymmetry, corresponding to spatial relation processing, exists for recognition of objects.