Erik C. Chang

Inhibition of return and the human frontal eye fields

Inhibition of return (IOR) is a bias against reorienting attention to a previously cued location. In this study, using single-pulse transcranial magnetic stimulation (TMS), we show that the human frontal eye fields (FEF) play a crucial role in the generation of IOR. When TMS was applied over the right FEF at a time interval after a visual cue but shortly before the target, IOR was modulated in the hemifield ipsilateral to the TMS such that responses to a previously cued target were no longer slower than responses to uncued targets. Control TMS over the superior parietal lobule, as well as TMS of the FEF shortly after the cue but well before the target, had no influence on IOR. We further show that the FEF is involved with visual selection as responses to targets appearing contralateral to the TMS of the FEF, but not the control site, were delayed. These results suggest that the FEF produces IOR by biasing attention and eye movements away from a previously attended location and facilitating target detection at novel locations.

Dissociable neural mechanisms for determining the perceived heaviness of objects and the predicted weight of objects during lifting: An fMRI investigation of the size-weight illusion

In size-weight (SW) illusions, people learn to scale their fingertip forces for lifting small and big objects of equal weight even though they fail to learn perceptually that both objects have the same weight. The question then arises as to what the separate neural mechanisms are for determining the perceived heaviness of objects and the predicted weight of these objects during lifting. To answer this question, we used fMRI to first identify areas that code for the size, weight, and density of objects using an adaptation paradigm. We then contrasted BOLD in the SW illusion condition in which subjects falsely perceived the smaller of two equally weighted objects as heavier versus a condition in which size and weight did not differ between objects. Sensory areas in the parietal and temporal cortex adapted to the size of objects and the primary motor area (M1) contralateral to the lifting hand adapted to the weight of objects. The ventral premotor area (PMv), which did not adapt to either the size or the weight of objects, adapted instead to the density of objects, and responded more when subjects falsely perceived differences in weight between objects in the SW illusion condition. Taken together, we conclude that the real-world properties of objects, such as size and weight, are computed by sensory areas and by M1 respectively, whereas the perceived heaviness of objects, presumably based on their apparent density, is computed by PMv, a higher-order area well placed to integrate sensory information about the size of objects and the weight of objects.

Locating the human frontal eye fields with transcranial magnetic stimulation

The variability in the location and function of the human frontal eye fields (FEFs) was assessed using transcranial magnetic stimulation (TMS). Ten subjects performed a saccadic eye movement task previously shown to be influenced by TMS of the FEFs. A sequence of points over the prefrontal cortex was stimulated until an effective site of the TMS was found that induced contralateral saccade delays. In 7 out of the 10 subjects, we were able to localize a region in the prefrontal cortex that when stimulated produced delays in the execution of contralateral saccadic eye movements. The location of this functionally defined FEF region across these subjects was approximately 1.5 cm anterior to the motor hand area, although there was considerable variability in this measure. In the remaining 3 subjects, no site within our circumscribed probing was found that when disrupted with TMS produced delays in contralateral saccadic eye movements. The inter-individual differences in the location and function of the FEFs highlights the importance of using functional as well as anatomical landmarks when attempting to localize brain structures.

The intermanual transfer of anticipatory force control in precision grip lifting is not influenced by the perception of weight.

Passing objects from one hand to the other occurs frequently in our daily life. What kind of information about the weight of the object is transferred between the holding and lifting hand? To examine this, we asked people to hold (and heft) an object in one hand and then pick it up with the other. The objects were presented in the context of a size–weight illusion: that is, two objects of different sizes but the same weight were used. One group of participants held one of the objects in their left hand and then picked it up with their right. Another group of participants simply picked up the objects from a table. Thus, the former group had on-line information about the weight of the object, whereas the latter did not. Both groups showed a strong and equivalent size–weight illusion throughout the experiment. At the same time, the group that lifted the objects from the hefting hand applied equal grip force to the small and large object right from the start; in contrast, the group lifting the objects from the table, initially applied more grip force to the large than to the small object before eventually applying the same force to both. In two additional groups, a delay period was imposed between the lifting of the first and the second hands. The force parameters employed by these last two groups were virtually identical to those used by the group that lifted the object directly from the other hand. These results suggest that the initial calibration of grip force uses veridical information about the weight of the object provided by the other hand. This veridical information about weight is available on-line and is retained in memory for later access. The perceived weight of the object is basically ignored in forming grasping forces.

The common magnitude code underlying numerical and size processing for action but not for perception

The interaction between numbers and action-related process has received increasing attention in the literature of numerical cognition. In the current study, two dual-task experiments were conducted to explore the interaction among numerical, prehension, and perceptual color/size judgments. The results revealed the commonality and distinctness of the magnitude representations that are involved in these tasks. Specifically, a photograph of a graspable object with a superimposed Arabic digit was presented in each trial. Participants were required to first judge the parity of the digit with a manual response while simultaneously planning a subsequent vocal response pertaining to the depicted object. When parity and action judgments were performed close in time, the compatibility effect between the numerical magnitude of the digit and the appropriate action (pinch vs. clutch) for the object was demonstrated in both manual and vocal responses. In contrast, such compatibility effect was absent when parity judgment was coupled with color-related or perceptual size judgment. The findings of the current study support the existence of a common magnitude code underlying numerical and non-numerical dimensions for action-related purposes, as proposed by the ATOM model (Walsh in Trends Cogn Sci 7:483–488, 2003). Furthermore, based on the selective presence of the compatibility effect, we argue that the interaction among different quantity dimensions conforms to the “dorsal-action and ventral-perception” organizational principle of the human brain.

Inhibition of return in perception and action

Inhibition of return (IOR) refers to the delay in responses to previously cued locations. Whether IOR influences perceptual and/or motor processes has been controversial. To determine IOR effects on perception and action, this study examined IOR in spatially directed hand reaching (Experiment 1) and spatial localization of targets with a mouse cursor (i.e., an indirect visuomotor mapping/perceptual task; Experiment 2). The reaction times showed delayed responses for targets appearing within the whole cued hemifield for both tasks. However, hypometric spatial biases were consistently found only with directed reaching. Spatial biases in the mouse localization task were indirectly influenced by IOR and distinct from those in the reaching task. The dissociation in spatial characteristics for directed reaching vs. perception suggests that the effects of IOR are task dependent, but may be more directly linked to the dorsal motor system.

Flicker-glare and visual-comfort assessments of light emitting diode billboards

This study investigated the discomfort glare produced by the high-brightness LED billboards in relation to four factors: flicker frequency, panel luminance, viewing angular sub-tense, and ambient illuminance. The results showed that visual comfort is not affected by ambient illuminance but by the other three factors. Also, interaction was found between luminance and viewing angle. The experimental data were curve fitted to construct visual comfort models of LED billboard displays. By modulating the operating conditions, comfort display with LED billboards can be achieved.

Bimanual Coordination Learning with Different Augmented Feedback Modalities and Information Types

Previous studies have shown that bimanual coordination learning is more resistant to the removal of augmented feedback when acquired with auditory than with visual channel. However, it is unclear whether this differential “guidance effect” between feedback modalities is due to enhanced sensorimotor integration via the non-dominant auditory channel or strengthened linkage to kinesthetic information under rhythmic input. The current study aimed to examine how modalities (visual vs. auditory) and information types (continuous visuospatial vs. discrete rhythmic) of concurrent augmented feedback influence bimanual coordination learning. Participants either learned a 90°-out-of-phase pattern for three consecutive days with Lissajous feedback indicating the integrated position of both arms, or with visual or auditory rhythmic feedback reflecting the relative timing of the movement. The results showed diverse performance change after practice when the feedback was removed between Lissajous and the other two rhythmic groups, indicating that the guidance effect may be modulated by the type of information provided during practice. Moreover, significant performance improvement in the dual-task condition where the irregular rhythm counting task was applied as a secondary task also suggested that lower involvement of conscious control may result in better performance in bimanual coordination.

Neural Mechanisms of Inhibitory Response in a Battlefield Scenario: A Simultaneous fMRI-EEG Study

The stop-signal paradigm has been widely adopted as a way to parametrically quantify the response inhibition process. To evaluate inhibitory function in realistic environmental settings, the current study compared stop-signal responses in two different scenarios: one uses simple visual symbols as go and stop signals, and the other translates the typical design into a battlefield scenario (BFS) where a sniper-scope view was the background, a terrorist image was the go signal, a hostage image was the stop signal, and the task instructions were to shoot at terrorists only when hostages were not present but to refrain from shooting if hostages appeared. The BFS created a threatening environment and allowed the evaluation of how participants’ inhibitory control manifest in this realistic stop-signal task. In order to investigate the participants’ brain activities with both high spatial and temporal resolution, simultaneous functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) recordings were acquired. The results demonstrated that both scenarios induced increased activity in the right inferior frontal gyrus (rIFG) and presupplementary motor area (preSMA), which have been linked to response inhibition. Notably, in right temporoparietal junction (rTPJ) we found both higher blood-oxygen-level dependent (BOLD) activation and synchronization of theta-alpha activities (4–12 Hz) in the BFS than in the traditional scenario after the stop signal. The higher activation of rTPJ in the BFS may be related to morality judgments or attentional reorienting. These results provided new insights into the complex brain networks involved in inhibitory control within naturalistic environments.

Monetary Reward and Punishment to Response Inhibition Modulate Activation and Synchronization Within the Inhibitory Brain Network

A reward or punishment can modulate motivation and emotions, which in turn affect cognitive processing. The present simultaneous functional magnetic resonance imaging-electroencephalography study examines neural mechanisms of response inhibition under the influence of a monetary reward or punishment by implementing a modified stop-signal task in a virtual battlefield scenario. The participants were instructed to play as snipers who open fire at a terrorist target but withhold shooting in the presence of a hostage. The participants performed the task under three different feedback conditions in counterbalanced order: a reward condition where each successfully withheld response added a bonus (i.e., positive feedback) to the startup credit, a punishment condition where each failure in stopping deduced a penalty (i.e., negative feedback), and a no-feedback condition where response outcome had no consequences and served as a control setting. Behaviorally both reward and punishment conditions led to significantly down-regulated inhibitory function in terms of the critical stop-signal delay. As for the neuroimaging results, increased activities were found for the no-feedback condition in regions previously reported to be associated with response inhibition, including the right inferior frontal gyrus and the pre-supplementary motor area. Moreover, higher activation of the lingual gyrus, posterior cingulate gyrus (PCG) and inferior parietal lobule were found in the reward condition, while stronger activation of the precuneus gyrus was found in the punishment condition. The positive feedback was also associated with stronger changes of delta, theta, and alpha synchronization in the PCG than were the negative or no-feedback conditions. These findings depicted the intertwining relationship between response inhibition and motivation networks.