Crosstalk characterization in homogeneous multicore fiber using discrete changes model under bidirectional propagation

For the first time, the discrete changes model has been explored for crosstalk estimation under the bidirectional propagation condition. Crosstalk characterization in homogeneous multicore fiber (MCF) has been discussed, with different crosstalk estimation methods, such as, conventional model for perfectly homogeneous core, discrete changes model for real homogeneous core, and propagation direction interleaving (PDI) approach for backward propagation. The forward crosstalk expression under bending and twisting conditions, derived by the authors, has been utilized to visualize the impact of fiber twisting over a wide range. Discrete changes model has been analyzed for backward crosstalk, in order to observe the XT behavior for deterministic bending and twisting effects. For the crosstalk analysis in bidirectional propagation, 12-core MCF has been used, with circular lattice and square lattice arrangements for single-mode propagation. Moreover, for optimization and crosstalk suppression, trench-assisted core and PDI technique have been used to obtain the significantly low crosstalk in limited cladding diameter of 200 µm. The influence of fiber length and wavelength has been exhibited on crosstalk performance. The worst crosstalk level, and relative spatial efficiency in these MCFs have been compared with recently reported works.

The Backward Crosstalk Effect Does Not Depend on the Degree of a Preceding Response Conflict

A common observation in dual tasking is a performance decrement in one or both tasks compared with single tasking. Besides, more specific interference occurs depending on certain characteristics of the two tasks. In particular, even Task 1 performance is often improved when responses in both tasks are compatible (e.g., both require left responses) compared to when they are incompatible: the compatibility-based backward crosstalk effect (BCE). Similar to what is observed for conflict tasks, the BCE is sequentially modulated: It is larger following compatible than following incompatible trials. Previous work has attributed this observation to adaptation effects triggered by response conflict arising during incompatible trials. In two experiments, we assessed sequential modulations following trials with different degrees of such a response conflict. In contrast to our expectations, a clear and sizeable sequential modulation was observed even under conditions where no BCE, and thus no empirical sign of an objective response conflict, was present in the previous trial. Therefore, our results show sequential modulations even without prior response conflict, which is not the (sole) trigger of sequential modulations accordingly. We discuss these results with regard to other potential triggers such as the subjective experience of conflict or difficulty, episodic retrieval, and repetitions of response combinations.

Disentangling stimulus and response compatibility as potential sources of backward crosstalk

In two experiments (N= 60 each), we investigated the locus of backward crosstalk effects in dual tasking. Specifically, we embedded the typical flanker task within a dual-task paradigm by assigning stimulus-response (S-R) rules to the flankers. In Experiment 1, participants were instructed to first respond to the center letter and only respond to the flanker if the center was a no-go stimulus (i.e., prioritized processing paradigm). Mapping condition was varied between-subjects to be either matched (i.e., same S-R rule for flankers as for center letters), reversed (i.e., opposite S-R rule for flankers), or neutral (i.e., different letters for flankers with separate S-R rules). The results indicated that the backward crosstalk effect was mainly driven by a stimulus-based compatibility, as indicated by a significant S2−R1 compatibility effect in the matched and reversed conditions, with little change in this effect between the matched and reversed conditions. Experiment 2 replicated and extended these findings to a psychological refractory period paradigm. The present findings suggest that in the matched and reversed conditions, there was only one S-R rule active at a time.