Visuospatial Perceptual Sequence Learning and Eye Movements

Can transcranial direct current stimulation (tDCS) of the cerebellum improve implicit social and cognitive sequence learning?

Accumulating evidence shows that the posterior cerebellum is involved in mentalizing inferences of social events by detecting sequence information in these events, and building and updating internal models of these sequences. By applying anodal and sham cerebellar transcranial direct current stimulation (tDCS) on the posteromedial cerebellum of healthy participants, and using a serial reaction time (SRT) task paradigm, the current study examined the causal involvement of the cerebellum in implicitly learning sequences of social beliefs of others (Belief SRT) and non-social colored shapes (Cognitive SRT). Apart from the social or cognitive domain differences, both tasks were structurally identical. Results of anodal stimulation (i.e., 2 mA for 20 min) during the social Belief SRT task, did not show significant improvement in reaction times, however it did reveal generally faster responses for the Cognitive SRT task. This improved performance could also be observed after the cessation of stimulation after 30 min, and up to one week later. Our findings suggest a general positive effect of anodal cerebellar tDCS on implicit non-social Cognitive sequence learning, supporting a causal role of the cerebellum in this learning process. We speculate that the lack of tDCS modulation of the social Belief SRT task is due to the familiar and overlearned nature of attributing social beliefs, suggesting that easy and automatized tasks leave little room for improvement through tDCS.

Inhibition of Eye Movements Disrupts Spatial Sequence Learning

Implicit sequence learning is an integral part of human experience, yet the nature of the mechanisms underlying this type of learning remains a matter of debate. In the current study, we provide a test for two accounts of implicit sequence learning, that is, one that highlights sequence learning in the absence of any motor responses (with suppressed eye movements) and one that highlights the relative contribution of the motor processes (i.e., eye movements) to learning. To adjudicate between these accounts and determine whether a motor response is a requisite process in sequence learning, we used anticipation measures to compare performance on the standard oculomotor serial reaction time (SRT) task and on a version of the SRT task where the eye movements were restricted during the learning phase. our results demonstrated an increased proportion of correct anticipations in the standard SRT task compared to the restricted-movement task.

Implicit perceptual learning of visual-auditory modality sequences

We examined perceptual modality sequence learning by presenting number words either visually (V) or auditorily (A). Manual responses were assigned to number identity, which was random, but the stimulus modalities followed a predictable 6-element sequence (e.g., VVAAVA). In two experiments, we assessed sequence-specific learning as the performance difference between the predictable sequence and a random transfer sequence. We expected learning benefits, but for visual trials we did not find any clear predictability benefits, and, surprisingly, for auditory trials we even found a general processing disadvantage (i.e., a predictability cost) for auditory trials (Experiment 1) or a cost-benefit pattern (Experiment 2, with equated shift rates in predictable and random sequences), with costs for auditory repetition trials and benefits for shifting to auditory processing. Hence, overall there was a general learning "cost" (Experiment 1) or a null net benefit of predictability for performance (Experiment 2). Together, the findings reveal a modality-specific sensitivity towards variations in shift frequency and modality predictability only for auditory trials, but there was no overall benefit of modality-specific sequence learning.

Is sequence awareness mandatory for perceptual sequence learning: An assessment using a pure perceptual sequence learning design

We examined the role of sequence awareness in a pure perceptual sequence learning design. Participants had to react to the target's colour that changed according to a perceptual sequence. By varying the mapping of the target's colour onto the response keys, motor responses changed randomly. The effect of sequence awareness on perceptual sequence learning was determined by manipulating the learning instructions (explicit versus implicit) and assessing the amount of sequence awareness after the experiment. In the explicit instruction condition (n = 15), participants were instructed to intentionally search for the colour sequence, whereas in the implicit instruction condition (n = 15), they were left uninformed about the sequenced nature of the task. Sequence awareness after the sequence learning task was tested by means of a questionnaire and the process-dissociation-procedure. The results showed that the instruction manipulation had no effect on the amount of perceptual sequence learning. Based on their report to have actively applied their sequence knowledge during the experiment, participants were subsequently regrouped in a sequence strategy group (n = 14, of which 4 participants from the implicit instruction condition and 10 participants from the explicit instruction condition) and a no-sequence strategy group (n = 16, of which 11 participants from the implicit instruction condition and 5 participants from the explicit instruction condition). Only participants of the sequence strategy group showed reliable perceptual sequence learning and sequence awareness. These results indicate that perceptual sequence learning depends upon the continuous employment of strategic cognitive control processes on sequence knowledge. Sequence awareness is suggested to be a necessary but not sufficient condition for perceptual learning to take place.

The influence of eye-movements on the development of a movement sequence representation during observational and physical practice

An experiment was conducted to examine the development of a movement sequence representation and the role of eye-movements during observational and physical practice. The task was to reproduce a 1300ms spatial-temporal pattern of a sequence of elbow flexions and extensions. An inter-manual transfer design with a retention and two effector transfer tests (contralateral limb) was used. The mirror transfer test required the same pattern of homologous muscle activation and a sequence of joint angles as experienced during the acquisition phase, and the non-mirror transfer test required the same visual-spatial pattern as performed or observed during acquisition. Participants were randomly assigned to one of four groups differing in eye-movements (free to use their eyes vs. instruction to fixate) and the practice type (observational practice vs. physical practice). The results indicated that permitting to use eye-movements facilitates sequence learning. This advantage was found on both practice types. The results of the transfer tests indicated that participants of the physical practice group who were permitted to use their eyes demonstrated superior transfer performance in the mirror transfer test, while participants in the observational practice group demonstrated better performance on the non-mirror transfer test. These findings indicated that eye-movements enhanced the development of a visual-spatial representation during observational practice as well as a motor representation during physical practice.

Magnifying visual target information and the role of eye movements in motor sequence learning

An experiment investigated the influence of eye movements on learning a simple motor sequence task when the visual display was magnified. The task was to reproduce a 1300 ms spatial-temporal pattern of elbow flexions and extensions. The spatial-temporal pattern was displayed in front of the participants. Participants were randomly assigned to four groups differing on eye movements (free to use their eyes/instructed to fixate) and the visual display (small/magnified). All participants had to perform a pre-test, an acquisition phase, a delayed retention test, and a transfer test. The results indicated that participants in each practice condition increased their performance during acquisition. The participants who were permitted to use their eyes in the magnified visual display outperformed those who were instructed to fixate on the magnified visual display. When a small visual display was used, the instruction to fixate induced no performance decrements compared to participants who were permitted to use their eyes during acquisition. The findings demonstrated that a spatial-temporal pattern can be learned without eye movements, but being permitting to use eye movements facilitates the response production when the visual angle is increased.

Does consolidation of visuospatial sequence knowledge depend on eye movements?

In the current study, we assessed whether visuospatial sequence knowledge is retained over 24 hours and whether this retention is dependent on the occurrence of eye movements. Participants performed two sessions of a serial reaction time (SRT) task in which they had to manually react to the identity of a target letter pair presented in one of four locations around a fixation cross. When the letter pair 'XO' was presented, a left response had to be given, when the letter pair 'OX' was presented, a right response was required. In the Eye Movements (EM) condition, eye movements were necessary to perform the task since the fixation cross and the target were separated by at least 9° visual angle. In the No Eye Movements (NEM) condition, on the other hand, eye movements were minimized by keeping the distance from the fixation cross to the target below 1° visual angle and by limiting the stimulus presentation to 100 ms. Since the target identity changed randomly in both conditions, no manual response sequence was present in the task. However, target location was structured according to a deterministic sequence in both the EM and NEM condition. Learning of the target location sequence was determined at the end of the first session and 24 hours after initial learning. Results indicated that the sequence learning effect in the SRT task diminished, yet remained significant, over the 24 hour interval in both conditions. Importantly, the difference in eye movements had no impact on the transfer of sequence knowledge. These results suggest that the retention of visuospatial sequence knowledge occurs alike, irrespective of whether this knowledge is supported by eye movements or not.

The effect of attentional load on implicit sequence learning in children and young adults

We investigated the effect of a secondary task on implicit sequence learning in children and young adults. A serial reaction time (SRT) task was administered to 8-to-10 year old children and 18-to-22 year old adults. Participants reacted to the location of a target presented in one of four locations on the screen with a spatially corresponding response key. Unknown to participants, the location at which the target appeared was structured according to a deterministic sequence. Occasionally, the black target dot was replaced by a red target dog. To assess the effect of attentional load on implicit sequence learning, half of the participants of each age group was assigned to the single task condition, while the other half executed the task under dual task conditions. Whereas participants in the single task condition could ignore the change in target identity, dual task participants additionally had to count the number of times the black dot was replaced by a red dog to increase the attentional load. Sequence learning was tested under single task conditions in both conditions. Z-transformed results indicate that young adults generally showed more sequence learning than children. Importantly, the secondary task had no effect on sequence learning in children, since children learned as much under dual task conditions as under single task conditions. Adults, on the other hand, showed a different result pattern, as they displayed more sequence learning under single task than under dual task conditions. We surmise that this result is due to the vainly attempt of adults, but not children, to integrate both sequences.