Algorithms for the automated correction of vertical drift in eye-tracking data.

A common problem in eye-tracking research is vertical drift-the progressive displacement of fixation registrations on the vertical axis that results from a gradual loss of eye-tracker calibration over time. This is particularly problematic in experiments that involve the reading of multiline passages, where it is critical that fixations on one line are not erroneously recorded on an adjacent line. Correction is often performed manually by the researcher, but this process is tedious, time-consuming, and prone to error and inconsistency. Various methods have previously been proposed for the automated, post hoc correction of vertical drift in reading data, but these methods vary greatly, not just in terms of the algorithmic principles on which they are based, but also in terms of their availability, documentation, implementation languages, and so forth. Furthermore, these methods have largely been developed in isolation with little attempt to systematically evaluate them, meaning that drift correction techniques are moving forward blindly. We document ten major algorithms, including two that are novel to this paper, and evaluate them using both simulated and natural eye-tracking data. Our results suggest that a method based on dynamic time warping offers great promise, but we also find that some algorithms are better suited than others to particular types of drift phenomena and reading behavior, allowing us to offer evidence-based advice on algorithm selection.

Connectivity of the Cingulate Sulcus Visual Area (CSv) in the Human Cerebral Cortex.

The human cingulate sulcus visual area (CSv) responds selectively to visual and vestibular cues to self-motion. Although it is more selective for visual self-motion cues than any other brain region studied, it is not known whether CSv mediates perception of self-motion. An alternative hypothesis, based on its location, is that it provides sensory information to the motor system for use in guiding locomotion. To evaluate this hypothesis we studied the connectivity pattern of CSv, which is completely unknown, with a combination of diffusion MRI and resting-state functional MRI. Converging results from the 2 approaches suggest that visual drive is provided primarily by areas hV6, pVIP (putative intraparietal cortex) and PIC (posterior insular cortex). A strong connection with the medial portion of the somatosensory cortex, which represents the legs and feet, suggests that CSv may receive locomotion-relevant proprioceptive information as well as visual and vestibular signals. However, the dominant connections of CSv are with specific components of the motor system, in particular the cingulate motor areas and the supplementary motor area. We propose that CSv may provide a previously unknown link between perception and action that serves the online control of locomotion.

Global Motion Processing in Human Visual Cortical Areas V2 and V3.

UNLABELLED: Global motion perception entails the ability to extract the central direction tendency from an extended area of visual space containing widely disparate local directions. A substantial body of evidence suggests that local motion signals generated in primary visual cortex (V1) are spatially integrated to provide perception of global motion, beginning in the middle temporal area (MT) in macaques and its counterpart in humans, hMT. However, V2 and V3 also contain motion-sensitive neurons that have larger receptive fields than those found in V1, giving the potential for spatial integration of motion signals. Despite this, V2 and V3 have been overlooked as sites of global motion processing. To test, free of local-global confounds, whether human V2 and V3 are important for encoding global motion, we developed a visual stimulus that yields a global direction yet includes all possible local directions and is perfectly balanced at the local motion level. We then attempted to decode global motion direction in such stimuli with multivariate pattern classification of fMRI data. We found strong sensitivity to global motion in hMT, as expected, and also in several higher visual areas known to encode optic flow. Crucially, we found that global motion direction could be decoded in human V2 and, particularly, in V3. The results suggest the surprising conclusion that global motion processing is a key function of cortical visual areas V2 and V3. A possible purpose is to provide global motion signals to V6. SIGNIFICANCE STATEMENT: Humans can readily detect the overall direction of movement in a flock of birds despite large differences in the directions of individual birds at a given moment. This ability to combine disparate motion signals across space underlies many aspects of visual motion perception and has therefore received considerable research attention. The received wisdom is that spatial integration of motion signals occurs in the cortical motion complex MT+ in both human and nonhuman primates. We show here that areas V2 and V3 in humans are also able to perform this function. We suggest that different cortical areas integrate motion signals in different ways for different purposes.

Neural correlates of finger gnosis.

Neuropsychological studies have described patients with a selective impairment of finger identification in association with posterior parietal lesions. However, evidence of the role of these areas in finger gnosis from studies of the healthy human brain is still scarce. Here we used functional magnetic resonance imaging to identify the brain network engaged in a novel finger gnosis task, the intermanual in-between task (IIBT), in healthy participants. Several brain regions exhibited a stronger blood oxygenation level-dependent (BOLD) response in IIBT than in a control task that did not explicitly rely on finger gnosis but used identical stimuli and motor responses as the IIBT. The IIBT involved stronger signal in the left inferior parietal lobule (IPL), bilateral precuneus (PCN), bilateral premotor cortex, and left inferior frontal gyrus. In all regions, stimulation of nonhomologous fingers of the two hands elicited higher BOLD signal than stimulation of homologous fingers. Only in the left anteromedial IPL (a-mIPL) and left PCN did signal strength decrease parametrically from nonhomology, through partial homology, to total homology with stimulation delivered synchronously to the two hands. With asynchronous stimulation, the signal was stronger in the left a-mIPL than in any other region, possibly indicating retention of task-relevant information. We suggest that the left PCN may contribute a supporting visuospatial representation via its functional connection to the right PCN. The a-mIPL may instead provide the core substrate of an explicit bilateral body structure representation for the fingers that when disrupted can produce the typical symptoms of finger agnosia.

Activity in the human superior colliculus relating to endogenous saccade preparation and execution.

In recent years a small number of studies have applied functional imaging techniques to investigate visual responses in the human superior colliculus (SC), but few have investigated its oculomotor functions. Here, in two experiments, we examined activity associated with endogenous saccade preparation. We used 3-T fMRI to record the hemodynamic activity in the SC while participants were either preparing or executing saccadic eye movements. Our results showed that not only executing a saccade (as previously shown) but also preparing a saccade produced an increase in the SC hemodynamic activity. The saccade-related activity was observed in the contralateral and to a lesser extent the ipsilateral SC. A second experiment further examined the contralateral mapping of saccade-related activity with a larger range of saccade amplitudes. Increased activity was again observed in both the contralateral and ipsilateral SC that was evident for large as well as small saccades. This suggests that the ipsilateral component of the increase in BOLD is not due simply to small-amplitude saccades producing bilateral activity in the foveal fixation zone. These studies provide the first evidence of presaccadic preparatory activity in the human SC and reveal that fMRI can detect activity consistent with that of buildup neurons found in the deeper layers of the SC in studies of nonhuman primates.

A representation of changing heading direction in human cortical areas pVIP and CSv.

When we move around in the environment, we continually change direction. Much work has examined how the brain extracts instantaneous direction of heading from optic flow but how changes in heading are encoded is unknown. Change could simply be inferred cognitively from successive instantaneous heading values, but we hypothesize that heading change is represented as a low-level signal that feeds into motor control with minimal need for attention or cognition. To test this, we first used functional MRI to measure activity in several predefined visual areas previously associated with processing optic flow (hMST, hV6, pVIP, and CSv) while participants viewed flow that simulated either constant heading or changing heading. We then trained a support vector machine (SVM) to distinguish the multivoxel activity pattern elicited by rightward versus leftward changes in heading direction. Some motion-sensitive visual cortical areas, including hMST, responded well to flow but did not appear to encode heading change. However, visual areas pVIP and, particularly, CSv responded with strong selectivity to changing flow and also allowed direction of heading change to be decoded. This suggests that these areas may construct a representation of heading change from instantaneous heading directions, permitting rapid and accurate preattentive detection and response to change.

Measuring response saturation in human MT and MST as a function of motion density.

The human brain areas MT and MST have been studied in great detail using fMRI with regards to their motion processing properties; however, to what extent this corresponds with single cell recordings remains to be fully described. Average response over human MT+ has been shown to increase linearly with motion coherence, similar to single cell responses. In response to motion density some single cell data however suggest a rapid saturation. We ask how the combination of these responses is reflected in the population response. We measured the blood oxygen level dependent (BOLD) response function of MT and MST using a motion density signal, comparing with area V1. We used spatially fixed apertures containing motion stimuli to manipulate the area covered by motion. We found that MT and MST responded above baseline to a very minimal amount of motion and showed a rather flat response to motion density, indicative of saturation. We discuss how this may be related to the size of the receptive fields and inhibitory interactions, although necessarily residual attention effects also need to be considered. We then compared different types of motion and found no difference between coherent and random motion at any motion density, suggesting that when combining response over several motion stimuli covering the visual field, a linear relationship of MT and MST population response as a function of motion coherence might not hold.

White matter tracts adjacent to the human cingulate sulcus visual area (CSv).

Human cingulate sulcus visual area (CSv) was first identified as an area that responds selectively to visual stimulation indicative of self-motion. It was later shown that the area is also sensitive to vestibular stimulation as well as to bodily motion compatible with locomotion. Understanding the anatomical connections of CSv will shed light on how CSv interacts with other parts of the brain to perform information processing related to self-motion and navigation. A previous neuroimaging study (Smith et al. 2018, Cerebral Cortex, 28, 3685-3596) used diffusion-weighted magnetic resonance imaging (dMRI) to examine the structural connectivity of CSv, and demonstrated connections between CSv and the motor and sensorimotor areas in the anterior and posterior cingulate sulcus. The present study aimed to complement this work by investigating the relationship between CSv and adjacent major white matter tracts, and to map CSv's structural connectivity onto known white matter tracts. By re-analysing the dataset from Smith et al. (2018), we identified bundles of fibres (i.e. streamlines) from the whole-brain tractography that terminate near CSv. We then assessed to which white matter tracts those streamlines may belong based on previously established anatomical prescriptions. We found that a significant number of CSv streamlines can be categorised as part of the dorsalmost branch of the superior longitudinal fasciculus (SLF I) and the cingulum. Given current thinking about the functions of these white matter tracts, our results support the proposition that CSv provides an interface between sensory and motor systems in the context of self-motion.

Effect of environmental factors on the abundance of decapod crustaceans from soft bottoms off southeastern Brazil.

This study investigated the importance of variations in environmental factors affecting the abundance patterns of decapods on the southeastern Brazilian coast. Sampling was carried out monthly from January 1998 through December 1999 in Ubatumirim and Mar Virado, Ubatuba region, using a commercial shrimp fishing boat equipped with double-rig nets. Six areas adjacent to rocky shores were chosen. Bottom-water samples were collected using a Nansen bottle, to measure the temperature and salinity. Sediment samples were also obtained by means of a Van Veen grab, for determination of texture and organic-matter content. The association of environmental factors with species abundance was evaluated by Canonical Correspondence Analysis (α = 0.05). Forty-one species of Decapoda were used in the multivariate analysis. The analysis indicated that sediment texture (phi) and bottom temperature were the main factors correlated (p < 0.05) with the spatial and temporal abundance of the species. Considering the study region as faunal transition zone, including a mixture of species of both tropical and subantarctic origin, the species responded differently to environmental factors, mainly temperature. It is conceivable that the decapods adjust their distribution according to their intrinsic physiological limitations, possibly as a result of the available resources.

Decoding rule search domain in the left inferior frontal gyrus.

Traditionally, the left hemisphere has been thought to extract mainly verbal patterns of information, but recent evidence has shown that the left Inferior Frontal Gyrus (IFG) is active during inductive reasoning in both the verbal and spatial domains. We aimed to understand whether the left IFG supports inductive reasoning in a domain-specific or domain-general fashion. To do this we used Multi-Voxel Pattern Analysis to decode the representation of domain during a rule search task. Thirteen participants were asked to extract the rule underlying streams of letters presented in different spatial locations. Each rule was either verbal (letters forming words) or spatial (positions forming geometric figures). Our results show that domain was decodable in the left prefrontal cortex, suggesting that this region represents domain-specific information, rather than processes common to the two domains. A replication study with the same participants tested two years later confirmed these findings, though the individual representations changed, providing evidence for the flexible nature of representations. This study extends our knowledge on the neural basis of goal-directed behaviors and on how information relevant for rule extraction is flexibly mapped in the prefrontal cortex.

Visual loss alters multisensory face maps in humans.

Topographically organised responses to visual and tactile stimulation are aligned in the ventral intraparietal cortex. The critical biological importance of this region, which is thought to mediate visually guided defensive movements of the head and upper body, suggests that these maps might be hardwired from birth. Here, we investigated whether visual experience is necessary for the creation and positioning of these maps by assessing the representation of tactile stimulation in congenitally and totally blind participants, who had no visual experience, and late and totally blind participants. We used a single-subject approach to the analysis to focus on the potential individual differences in the functional neuroanatomy that might arise from different causes, durations and sensory experiences of visual impairment among participants. The overall results did not show any significant difference between congenitally and late blind participants; however, single-subject trends suggested that visual experience is not necessary to develop topographically organised maps in the intraparietal cortex, whilst losing vision disrupted topographic maps' integrity and organisation. These results discussed in terms of brain plasticity and sensitive periods.

An fMRI Investigation of Preparatory Set in the Human Cerebral Cortex and Superior Colliculus for Pro- and Anti-Saccades.

Previous studies have identified several cortical regions that show larger BOLD responses during preparation and execution of anti-saccades than pro-saccades. We confirmed this finding with a greater BOLD response for anti-saccades than pro-saccades during the preparation phase in the FEF, IPS and DLPFC and in the FEF and IPS in the execution phase. We then applied multi-voxel pattern analysis (MVPA) to establish whether different neural populations are involved in the two types of saccade. Pro-saccades and anti-saccades were reliably decoded during saccade execution in all three cortical regions (FEF, DLPFC and IPS) and in IPS during saccade preparation. This indicates neural specialization, for programming the desired response depending on the task rule, in these regions. In a further study tailored for imaging the superior colliculus in the midbrain a similar magnitude BOLD response was observed for pro-saccades and anti-saccades and the two saccade types could not be decoded with MVPA. This was the case both for activity related to the preparation phase and also for that elicited during the execution phase. We conclude that separate cortical neural populations are involved in the task-specific programming of a saccade while in contrast, the SC has a role in response preparation but may be less involved in high-level, task-specific aspects of the control of saccades.

Cortical hyperexcitability and sensitivity to discomfort glare.

It is well established that there are two main aspects to glare, the visual impairment and the discomfort, known as disability and discomfort glare, respectively. In contrast to the case of disability glare we understand very little about the underlying mechanisms or physiology of discomfort glare. This study attempts to elucidate the neural mechanisms involved using fMRI and glare sources with controlled levels of retinal illuminance. Prior to carrying out the fMRI experiment, we determined each participant's discomfort glare threshold. The participants were then divided into two groups of equal size based on their ranked sensitivity to discomfort glare, a low and high sensitivity group. In the fMRI experiment each participant was presented with three levels of glare intensity whilst simultaneously required to carry out a simple behavioral task. We compared BOLD responses between the two groups and found that the group more sensitive to glare had an increased response that was localized at three discrete, bilateral cortical locations: one in the cunei, one in the lingual gyri and one in the superior parietal lobules. This increased response was present for all light levels tested, whether or not they were intense enough to cause discomfort glare. Based on the results, we present the case that discomfort glare may be a response to hyperexcitability or saturation of visual neurons.