Simultaneous completions of modal and amodal figures: Visual evoked potentials reveal asymmetrical interference effects

Modal and amodal completion processes are thought to affect the emergence and the potency of each other. To see whether one dominates over the other, we measured the Npd, that is, the negativity of visual-evoked potentials whose amplitude increases with perceptual difficulty. In the first experiment, the Npds to illusory (modal) squares and diamonds placed over amodal diamonds and squares, respectively, were found to be greater when targets were the amodal figures than when targets were the modal figures, thus suggesting that modal figures created more interference. A second experiment showed that greater Npds were specific to interference and not to the greater difficulty at focusing on amodal figures rather than on modal figures. A third experiment showed that the interference also occurs with real figures in replacement of modal ones. Overall, the results suggest a certain dominance of modal completion over amodal completion when both occur in the same display.     

A kinematic and dynamic comparison of surface and underwater displacement in high level monofin swimming

Fin swimming performance can be divided into underwater and surface water races. World records are about 10% faster for underwater swimming vs. surface swimming, but little is known about the advantage of underwater swimming for monofin swimming. Some authors reported that the air–water interface influences the kinematics and leads to a narrow vertical amplitude of the fin. On the one hand, surface swimming is expected to affect drag parameters (cross-sectional area (S) and active drag (AD)) when compared to underwater swimming. On the other hand, the surface swimming technique may also affect efficiency (η_F). The aim of this study is therefore to evaluate and compare drag parameters and efficiency during underwater and surface swimming. To this end, 12 international level monofin swimmers were measured during both underwater and surface swimming. Kinematic parameters (both dimensional and non-dimensional), η_F (calculated according to the Elongated-Body Theory), and AD (computed with Velocity Perturbation Method) were calculated for an underwater and a surface fin swimming trial, performed at maximal speed. As expected, results showed significantly lower velocities during surface swimming vs. underwater  = 2.5 m s⁻¹ vs.  = 2.36 m s⁻¹, p < .01). Velocities during underwater and surface swimming were strongly correlated (r = .97, p < .01). Underwater swimming was also associated with higher vertical amplitudes of the fin compared to surface swimming ( = 0.55 m vs. ) = 0.46 m, p < .01). Length-specific amplitudes (A_under/L_b) were in the order of 20% during underwater swimming as for undulating fish, and significantly higher than during surface swimming (A_surf/L_b = 17%, p < .01). Efficiency for surface swimming was about 6% lower than for underwater swimming ( = 0.79 vs.  = 0.74, p < .01). This decrease could be associated with an increase in swimming frequency for surface swimming ( = 2.15 Hz vs.  = 2.08 Hz, p < .01). Active drag during surface swimming was about 7% higher than for underwater swimming ( = 78.9 N vs.  = 84.7 N, p < .01). A significantly smaller cross-sectional area for surface swimming ( = 0.053 m² vs.  = 0.044 m², p < .01) and higher drag coefficient for surface swimming ( = 0.47 vs.  = 0.69, p < .01) were measured. Finally, correlation between cross-sectional area and vertical amplitude of the fin was reported for both underwater and surface swimming. These results suggest that the performance improvement during underwater swimming is not only linked to a wave drag reduction effect but also to a specific swimming technique due to the free surface.     

Electrophysiological evidence of central interference in the control of visuospatial attention

Visuospatial attention can be deployed to different locations in space without movement of the eyes. A large body of human electrophysiological studies reveals enhanced sensory-perceptual responses to stimuli that appear at an attended location. However, it is not clear that the mechanisms that underlie visuospatial attention are under the control of attention mechanisms that limit central processing in multiple-task situations. We investigated this question by incorporating a visual task that required the deployment of visuospatial attention as the second task of psychological refractory period (PRP) dual-task paradigms. The N2pc component of the event-related potential was used as an electrophysiological index of the moment-by-moment deployment of visuospatial attention to monitor when and where observers were attending while they performed concurrent central processing known to cause the PRP effect. Electrophysiological evidence shows that central processing interfered with the N2pc, suggesting that visuospatial attention is under the control of capacity-limited central mechanisms.     

Memory and consciousness: trace distinctiveness in memory retrievals

The aim of this article was to provide experimental evidence that classical dissociation between levels of consciousness associated with memory retrieval (i.e., implicit or explicit) can be explained in terms of task dependency and distinctiveness of traces. In our study phase, we manipulated the level of isolation (partial vs. global) of the memory trace by means of an isolation paradigm (isolated words among non-isolated words). We then tested these two types of isolation in a series of tasks of increasing complexity: a lexical decision task, a recognition task, and a free recall task. The main result of this study was that distinctiveness effects were observed as a function of the type of isolation (level of isolation) and the nature of the task. We concluded that trace distinctiveness improves subsequent access to the trace, while the level of trace distinctiveness also appears to determine the possibility of conscious or explicit retrieval.