Rightward Eye Movements Research Articles

Eye-movements reveal the serial position of the attended item in verbal working memory.

The problem of how the mind can retain sequentially organized information has a long research tradition that remains unresolved. While various computational models propose a mechanism of binding serial order information to position markers, the representational nature and processes that operate on these position markers are not clear. Recent behavioral work suggests that space is used to mark positions in serial order and that this process is governed by spatial attention. Based on the assumption that brain areas controlling spatial attention are also involved in saccadic planning, we continuously tracked the eye-movements as a direct measure of the spatial attention during retrieval from a verbal WM sequence. Participants memorized a sequence of auditory numbers. During retention, they heard a number-cue that did or did not belong to the memorized set. After this number-cue, a target-beep could be presented to which they had to respond if the number-cue belonged to the memorized sequence. In Experiment 1, the target-beep was either presented to the left or right ear, and in Experiment 2 bilaterally (removing any spatial aspect). We tested the hypothesis that systematic eye-movements are made when people retrieve items of sequences of auditory words and found that the retrieval of begin items resulted in leftward eye-movements and the retrieval of end items in rightward eye-movements. These observations indicate that the oculomotor system is also involved in the serial order processes in verbal WM thereby providing a promising novel approach to get insight into abstract cognitive processes.

The effect of leftward bias on visual attention for driving tasks

The leftward bias of driving visual attention has been found to explain the role of driving experience in the visual attention strategy; even though the results reported in the literature are not always consistent. This study aims to explore the driving attention characteristics and the eye movement patterns by using a simulated driving experiment in conjunction with an eye-tracker device. 31 young inexperienced drivers (undergraduate students, average age 21) and 30 old experienced drivers (taxi drivers, average age 36) took part in the experiment. Results show that the eye movement patterns of the drivers have certain similarity in the occurrence of subtle asymmetries of visual attention favouring left space (the direction of the driving in the experiment was right-side) and that they are related to the right hemisphere specialization for spatial attention. However, in the more experienced drivers the leftward eye movement tends to shift toward the centre or even rightward to pay attention to the hazard events on road. These results suggest that inexperienced drivers are initially aroused by natural biological leftward visual attention and likely to develop central and rightward eye movement strategy for safety diving purpose. The implications of this study suggest that, despite the existence of natural visual attention bias, the left asymmetries in visual scan in inexperienced drivers still can be modified by driving trainings that focus on the hazard situation on road.

Spatial Attention Shifts in Addition and Subtraction Arithmetic: Evidence of Eye Movement.

Recently, it has been proposed that solving addition and subtraction problems can evoke horizontal shifts of spatial attention. However, prior to this study, it remained unclear whether orienting shifts of spatial attention relied on actual arithmetic processes (i.e., the activated magnitude) or the semantic spatial association of the operator. In this study, spatial–arithmetic associations were explored through three experiments using an eye tracker, which attempted to investigate the mechanism of those associations. Experiment 1 replicated spatial–arithmetic associations in addition and subtraction problems. Experiments 2 and 3 selected zero as the operand to investigate whether these arithmetic problems could induce shifts of spatial attention. Experiment 2 indicated that addition and subtraction problems (zero as the second operand, i.e., 2 + 0) do not induce shifts of spatial attention. Experiment 3 showed that addition and subtraction arithmetic (zero as the first operand, i.e., 0 + 2) do facilitate rightward and leftward eye movement, respectively. This indicates that the operator alone does not induce horizontal eye movement. However, our findings support the idea that solving addition and subtraction problems is associated with horizontal shifts of spatial attention.

Trans-saccadic memory after right parietal brain damage

IntroductionSpatial remapping, the process of updating information across eye movements, is an important mechanism for trans-saccadic perception. The right posterior parietal cortex (PPC) is a region that has been associated most strongly with spatial remapping. The aim of the project was to investigate the effect of damage to the right PPC on direction specific trans-saccadic memory. We compared trans-saccadic memory performance for central items that had to be remembered while making a left- versus rightward eye movement, or for items that were remapped within the left versus right visual field. MethodsWe included 9 stroke patients with unilateral right PPC lesions and 31 healthy control subjects. Participants memorized the location of a briefly presented item, had to make one saccade (either towards the left or right, or upward or downward), and subsequently had to decide in what direction the probe had shifted. We used a staircase to adjust task difficulty (i.e., the distance between the memory item and probe). Bayesian repeated measures ANOVAs were used to compare left versus right eye movements and items in the left versus right visual field. ResultsIn both conditions, patients with right PPC damage showed worse trans-saccadic memory performance compared to healthy control subjects (for the condition with left- and rightward gaze shifts, BF10 = 3.79; and when items were presented left or right, BF10 = 6.77), regardless of the direction of the gaze or the initial location of the memory item. At the individual level, none of the patients showed a direction specific deficit after leftward versus rightward saccades, whereas two patients showed worse performance for items in the left versus right visual field. ConclusionDamage in the right PPC did not lead to gaze direction specific impairments in trans-saccadic memory, but instead caused more general spatial memory impairments.

No direction specific costs in trans-saccadic memory

Even though we frequently execute saccades, we perceive the external world as coherent and stable. An important mechanism of trans-saccadic perception is spatial remapping: the process of updating information across eye movements. Previous studies have indicated a right hemispheric dominance for spatial remapping, which has been proposed to translate into enhanced trans-saccadic memory for locations that are remapped into the right compared to the left hemisphere in healthy participants. Previous study designs suffered from several limitations, however (i.e. multiple eye movements had to be made instead of one, fixations were not controlled for, and ceiling effects were likely present). We therefore compared accuracy of trans-saccadic memory for central items after left- versus rightward eye movements, and secondary, for items that were remapped within the left versus right visual field. Participants memorized the location of a briefly presented item, made one saccade, and subsequently decided in what direction the item had shifted. We used a staircase to adjust task difficulty. Bayesian repeated measures ANOVAs were used to compare between left versus right eye movements and items in the left versus right visual field. We found most evidence against directional differences in trans-saccadic memory (BF10 = 0.23). We found some evidence suggestive of enhanced trans-saccadic memory for items that were remapped within the left compared to the right visual field (BF10 = 4.00). The latter result could be explained by a leftward spatial attention bias. As such, the hypothesized right hemispheric dominance for spatial remapping does not result in asymmetric trans-saccadic memory capacities in healthy participants.

Time course of overt attentional shifts in mental arithmetic: Evidence from gaze metrics.

Processing numbers induces shifts of spatial attention in probe detection tasks, with small numbers orienting attention to the left and large numbers to the right side of space. This has been interpreted as supporting the concept of a mental number line with number magnitudes ranging from left to right, from small to large numbers. Recently, the investigation of this spatial-numerical link has been extended to mental arithmetic with the hypothesis that solving addition or subtraction problems might induce attentional displacements, rightward or leftward, respectively. At the neurofunctional level, the activations elicited by the solving of additions have been shown to resemble those induced by rightward eye movements. However, the possible behavioural counterpart of these activations has not yet been observed. Here, we investigated overt attentional shifts with a target detection task primed by addition and subtraction problems (2-digit ± 1-digit operands) in participants whose gaze orientation was recorded during the presentation of the problems and while calculating. No evidence of early overt attentional shifts was observed while participants were hearing the first operand, the operator or the second operand, but they shifted their gaze towards the right during the solving step of addition problems. These results show that gaze shifts related to arithmetic problem solving are elicited during the solving procedure and suggest that their functional role is to access, from the first operand, the representation of the result.

Reading comprehension and its relationship with working memory capacity when reading horizontally scrolling text.

The horizontally scrolling format, where text is presented in a single line drifting right to left, is relatively commonly used to display text on digital screens. This format presents a potentially challenging reading situation as the text must be followed smoothly to the left (to track individual words) while rightward eye movements are made as usual to progress through the text. This conflict may reduce attention allocated to upcoming text. Returning to previously encountered text is also more difficult with this format. Here, a sustained reading comprehension task was used to compare performance with horizontally scrolling and multi-line static text formats. Results showed that literal comprehension can be reasonably well maintained with scrolling text, although small decrements are seen at faster scrolling rates. However, they indicated that this format makes it more difficult to answer questions requiring an inference to be made. The contribution of working memory capacity and the impact of display speed on these effects were considered. These findings have implications for the application of this format in digital media and also more widely for the conditions required for successful in-depth reading comprehension with any text format.

Effects of Parkinson's disease on cognitive action control: Insights on impulsive response tendencies using an oculomotor Simon task

Objectives: Cognitive action control allows suppressing automatic activation and producing a controlled response when conflicts arise. This process is modulated by the basal ganglia and recent studies have shown that it was impaired in Parkinson's disease (PD). This study gives insights regarding the effect of PD on cognitive action and more precisely on impulsive responses. Methods: 40 patients with PD with no cognitive impairment and 40 healthy controls (HC) underwent an oculomotor Simon task in which they were required to make a leftward or rightward eye movement according to the color of a target and to ignore its location. The two dimensions of the stimuli created congruent (color and location activating the same response) and incongruent (color and location activating conflicting responses) trials. Results were analyzed using distributional analysis according to the activation-suppression model. Results: PD patients had a greater congruence effect on both reaction time and accuracy rate demonstrating a greater difficulty to resolve conflicts. Distributional analysis revealed that PD patients made more fast errors than HC. The rate of impulsive errors was further correlated to the Barrat Impulsiveness Scale (BIS) scores. When they responded slower, PD patients were also impaired compared to HC. Conclusions: Our results show that both the automatic and controlled routes involved in the cognitive action control are affected in PD. Furthermore, impulsive response tendencies in PD measured by a conflict task seems related to behavioral impulsivity. Therefore, conflict tasks could be used to further study impulsivity in PD and its ability to detect early troubles should be investigated

Sensory attenuation and Parkinson's disease: a new pathophysiological framework of bradykinesia

s / Parkinsonism and Related Disorders 22 (2016) e7ee10 e9 Objectives: Cognitive action control allows suppressing automatic activation and producing a controlled response when conflicts arise. This process is modulated by the basal ganglia and recent studies have shown that it was impaired in Parkinson's disease (PD). This study gives insights regarding the effect of PD on cognitive action and more precisely on impulsive responses. Methods: 40 patients with PD with no cognitive impairment and 40 healthy controls (HC) underwent an oculomotor Simon task in which they were required tomake a leftward or rightward eyemovement according to the color of a target and to ignore its location. The two dimensions of the stimuli created congruent (color and location activating the same response) and incongruent (color and location activating conflicting responses) trials. Results were analyzed using distributional analysis according to the activation-suppression model. Results: PD patients had a greater congruence effect on both reaction time and accuracy rate demonstrating a greater difficulty to resolve conflicts. Distributional analysis revealed that PD patients made more fast errors than HC. The rate of impulsive errors was further correlated to the Barrat Impulsiveness Scale (BIS) scores. When they responded slower, PD patients were also impaired compared to HC. Conclusions: Our results show that both the automatic and controlled routes involved in the cognitive action control are affected in PD. Furthermore, impulsive response tendencies in PD measured by a conflict task seems related to behavioral impulsivity. Therefore, conflict tasks could be used to further study impulsivity in PD and its ability to detect early troubles should be investigated. OP 1.30.20. SENSORY ATTENUATION AND PARKINSON'S DISEASE: A NEW PATHOPHYSIOLOGICAL FRAMEWORK OF BRADYKINESIA Antonella Macerollo, Jui-Cheng Chen, Prasad Korlipara, Thomas Foltynie, John Rothwell, Mark Edwards, James Kilner. UCL, London,

Dynamic mental number line in simple arithmetic.

Studies have found that spatial-numerical associations could extend to arithmetic. Addition leads to rightward shift in spatial attention while subtraction leads to leftward shift (e.g., Knops et al. 2009; McCrink et al. 2007; Pinhas & Fischer 2008), which is consistent with the hypothesis of static mental number line (MNL) for arithmetic. The current investigation tested the hypothesis of dynamic mental number line which was shaped by the relative magnitudes of two operands in simple arithmetic. Horizontal and vertical electrooculograms (HEOG and VEOG) during simple arithmetic were recorded. Results showed that the direction of eye movements was dependent on the relative magnitudes of two operands. Subtraction was associated with larger rightward eye movements than addition (Experiment 1), and smaller-operand-first addition (e.g., 2+9) was associated with larger rightward eye movement than larger-operand-first addition (e.g., 9+2) only when the difference of two operands was large (Experiment 2). The results suggest that the direction of the mental number line could be dynamic during simple arithmetic, and that the eyes move along the dynamic mental number line to search for solutions.

Oculomotor control after hemidecortication: A single hemisphere encodes corollary discharges for bilateral saccades

Patients who have had a cerebral hemisphere surgically removed as adults can generate accurate leftward and rightward saccadic eye movements, a task classically thought to require two hemispheres each controlling contralateral saccades. Here, we asked whether one hemisphere can generate sequences of saccades, the success of which requires the use of corollary discharges. Using a double-step saccade paradigm, we tested two hemidecorticate subjects who, by definition, are contralesionally hemianopic. In experiment 1, two targets, T1 and T2, were flashed in their seeing hemifield and subjects had to look in the dark to T1, then T2. In experiment 2, only one target was flashed; before looking at it, the subject had first to saccade voluntarily elsewhere. Both subjects were able to complete the tasks, independent of first and second saccade direction and whether the saccades were voluntarily or visually triggered. Both subjects displayed a strategy, typical in hemianopia, of making multiple-step saccades and placing, at overall movement-end, the recalled locations of T1 and T2 on off-foveal locations in their seeing hemifield, in a retinal area typically spanning a 5–15° window, depending on the subject, trial type and target eccentricity. In summary, a single hemisphere monitored the amplitude and direction of the first multiple-step saccade sequence bilaterally, and combined this information with the recalled initial retinotopic location of T2 (no longer visible) to generate a correct target-directed second saccade sequence in the dark. Unexpectedly, our hemidecorticate subjects performed better on the double-step task than subjects with isolated unilateral parietal lesions, reported in the literature to have marked deficiencies in monitoring contralesional saccadic eye movements. Thus, plasticity-dependent mechanisms that lead to recovery of function after hemidecortication are different than those deployed after smaller lesions. This implies a reconsideration of the classical links between behavioural deficits and discrete cortical lesions.

A deficit of spatial remapping in constructional apraxia after right-hemisphere stroke

Constructional apraxia refers to the inability of patients to copy accurately drawings or three-dimensional constructions. It is a common disorder after right parietal stroke, often persisting after initial problems such as visuospatial neglect have resolved. However, there has been very little experimental investigation regarding mechanisms that might contribute to the syndrome. Here, we examined whether a key deficit might be failure to integrate visual information correctly from one fixation to the next. Specifically, we tested whether this deficit might concern remapping of spatial locations across saccades. Right-hemisphere stroke patients with constructional apraxia were compared to patients without constructional problems and neurologically healthy controls. Participants judged whether a pattern shifted position (spatial task) or changed in pattern (non-spatial task) across two saccades, compared to a control condition with an equivalent delay but without intervening eye movements. Patients with constructional apraxia were found to be significantly impaired in position judgements with intervening saccades, particularly when the first saccade of the sequence was to the right. The importance of these remapping deficits in constructional apraxia was confirmed through a highly significant correlation between saccade task performance and constructional impairment on standard neuropsychological tasks. A second study revealed that even single saccades to the right can impair constructional apraxia patients' perception of location shifts. These data are consistent with the view that rightward eye movements result in loss of remembered spatial information from previous fixations, presumably due to constructional apraxia patients' damage to the right-hemisphere regions involved in remapping locations across saccades. These findings provide the first evidence for a deficit in remapping visual information across saccades underlying right-hemisphere constructional apraxia.

Learning Substrates in the Primate Prefrontal Cortex and Striatum: Sustained Activity Related to Successful Actions

Learning from experience requires knowing whether a past action resulted in a desired outcome. The prefrontal cortex and basal ganglia are thought to play key roles in such learning of arbitrary stimulus-response associations. Previous studies have found neural activity in these areas, similar to dopaminergic neurons' signals, that transiently reflect whether a response is correct or incorrect. However, it is unclear how this transient activity, which fades in under a second, influences actions that occur much later. Here, we report that single neurons in both areas show sustained, persistent outcome-related responses. Moreover, single behavioral outcomes influence future neural activity and behavior: behavioral responses are more often correct and single neurons more accurately discriminate between the possible responses when the previous response was correct. These long-lasting signals about trial outcome provide a way to link one action to the next and may allow reward signals to be combined over time to implement successful learning.

Recruitment of an Area Involved in Eye Movements During Mental Arithmetic

Throughout the history of mathematics, concepts of number and space have been tightly intertwined. We tested the hypothesis that cortical circuits for spatial attention contribute to mental arithmetic in humans. We trained a multivariate classifier algorithm to infer the direction of an eye movement, left or right, from the brain activation measured in the posterior parietal cortex. Without further training, the classifier then generalized to an arithmetic task. Its left versus right classification could be used to sort out subtraction versus addition trials, whether performed with symbols or with sets of dots. These findings are consistent with the suggestion that mental arithmetic co-opts parietal circuitry associated with spatial coding.

Active linear head motion improves dynamic visual acuity in pursuing a high-speed moving object

We usually move both our eyes and our head when pursuing a high-speed moving object. However, the vestibulo-ocular reflex (VOR), evoked by head motion, seems to disturb smooth pursuit eye movement because the VOR stabilizes the gaze against head motion. To determine whether head motion is advantageous for pursuing a high-speed moving object, we examined dynamic visual acuity (DVA) for a high-speed (80 degrees /s) rightward moving object with and without active linear rightward head motion (HM) at a maximum of 50 cm/s in nine healthy subjects. Furthermore, we analyzed eye and head movements to investigate the contribution of linear VOR (LVOR) and smooth eye movement under these conditions. In most subjects, active linear head motion improved DVA for a high-speed moving object. Subjects with higher DVA scores under HM had robust rightward gaze (eye + head) velocities (>60 cm/s), i.e., rightward smooth eye movements (>10 degrees /s). With the head stationary (HS), faster smooth eye movements (>40 degrees /s) were generated when the subjects pursued a high-speed moving object. They also showed anticipatory smooth eye movements under conditions HM and HS. However, the level of suppression of their LVOR abilities was equal to that of the others. These results suggest that the ability to generate anticipatory smooth pursuit eye movements for following a high-speed moving object against the LVOR is a determining factor for improvement of DVA under HM.

Scaling of the Fore-Aft Vestibulo-Ocular Reflex by Eye Position During Smooth Pursuit

An eye position signal scales the amplitude of compensatory eye velocity in the translational vestibulo-ocular reflex (TVOR). To investigate the origin of such a modulatory signal, we studied the kinematics of the fore-aft TVOR as rhesus monkeys pursued a horizontally moving target at velocities between 0.5 and 30 degrees /s. We found that the "V-shaped" curve of the fore-aft TVOR amplitude as a function of eye position was shifted opposite to the direction of pursuit eye movement. As a result, the tip of the V-shaped curve that occurred close to zero eye position during steady-state fixation was shifted to the right during leftward pursuit and to the left during rightward pursuit eye movements. The faster the pursuit velocity the larger the observed shift. These results suggest that the scaling of the TVOR can precede actual eye position changes by several tens of milliseconds, which averaged 169 +/- 87 ms in three rhesus monkeys. Thus, central motor commands, rather than low-level efference copy or proprioceptive information, may be the signals scaling TVOR amplitude.

Optimal Decisions: From Neural Spikes, through Stochastic Differential Equations, to Behavior

There is increasing evidence from in vivo recordings in monkeys trained to respond to stimuli by making left- or rightward eye movements, that firing rates in certain groups of neurons in oculo-motor areas mimic drift-diffusion processes, rising to a (fixed) threshold prior to movement initiation. This supplements earlier observations of psychologists, that human reaction-time and error-rate data can be fitted by random walk and diffusion models, and has renewed interest in optimal decision-making ideas from information theory and statistical decision theory as a clue to neural mechanisms. We review results from decision theory and stochastic ordinary differential equations, and show how they may be extended and applied to derive explicit parameter dependencies in optimal performance that may be tested on human and animal subjects. We then briefly describe a biophysically-based model of a pool of neurons in locus coeruleus, a brainstem nucleus implicated in widespread norepinephrine release. This neurotransmitter can effect transient gain changes in cortical circuits of the type that the abstract drift-diffusion analysis requires. We also describe how optimal gain schedules can be computed in the presence of time-varying noisy signals. We argue that a rational account of how neural spikes give rise to simple behaviors is beginning to emerge.

Leaky neural integration observed in square-wave jerks

Purpose To clarify the neuronal mechanism for the square-wave jerks (SWJs). Methods A 66-year-old man presented with oscillatory eye movements. He showed horizontal nystagmus in rightward gaze and SWJs during fixation at straight ahead. We recorded his eye movements with search coil methods and quantitatively analyzed them. Results Visually guided rightward saccades were followed by exponential drifts with average time constants of 0.3–1.0 second, indicating a leaky rightward velocity-to-position integrator. Amplitude of SWJs ranged from 0.5 to 2.5° and average intersaccadic interval was 0.2 seconds. In addition, exponential drifts similar to those observed after visually guided saccades were observed in the SWJs. Rightward fast eye movements of SWJs were followed by exponential drifts lasting for 0.2 seconds with average time constant (±SD) of 0.7±0.3 seconds. Conclusions Position signals after visually guided saccades and SWJs were outputs of the identical velocity-to-position integrator. SWJs are generated by the neural circuits involving a pulse generator and a velocity-to-position integrator.

Vertical and Horizontal Eye Displacement During Static Pitch and Roll Postures

The positions of both eyes were measured objectively in the dark following "look straight ahead" instructions for 16 subjects at 27 combinations of static pitch and roll postures over 360 degrees of space, using an infrared video technique. Shifts in vertical version, or the doll reflex, varied sinusoidally with pitch and roll angle. At 0 degree roll, the average response has a peak-to-trough amplitude of 9.28 degrees and is symmetric about a downward eye position of 4.63 degrees. The proposed Dual Otolith Model (DOM), based on a combination of utricular and saccular inputs, provided excellent fits to the present data (R2 = 0.876) and to the data of previous studies (R2 = 0.916 to 0.994). Deviations in horizontal version varied sinusoidally with roll angle, with no significant effect of pitch angle. In general, clockwise (right-ear-down) rolls produced rightward eye movements, and counterclockwise (left-ear-down) rolls produced leftward eye movements. The average versions were symmetric about a leftward eye position of 1.14 degrees, with a peak-to-trough amplitude of 3.76 degrees. The data were well represented by the proposed Horizontal Version Model (HVM; R2 = 0.796), which depended only on utricular input.

The complementary relationship between waking and REM sleep in the oculomotor system: an increase of rightward saccades during waking causes a decrease of rightward eye movements during REM sleep

Since an inverse relationship between waking and REM sleep eye movements (EMs) has been found with respect to frequency, amplitude and direction of EMs, we evaluated variations in the percentages of horizontal rapid eye movements (REMs) during REM sleep after having increased rightward saccades during waking by means of a unilateral tachistoscopic visual test administered prior to sleep. In another condition subjects were given the same 4 h testing condition prior to sleep, the only difference being that they were instructed not to move their gaze; therefore only “attentional movements” were possible. This condition served as a control for the role of oculomotor activity in the complementary relationship between waking and REM sleep eye movements. The actual increase of rightward saccades during waking resulted in a significant decrease of rightward REMs. This effect has been observed only in the condition in which rightward eye movements were increased and it is specific for REMs of amplitude similar to those which were increased during waking by the lateralized test.