Results from three experiments using spatial forced-choice techniques show that an illusory contour improves the detectability of a spatially superimposed, 1pixel-thin subthreshold line of either contrast polarity. Furthermore, the subthreshold line is found to enhance the visibility of an illusory contour bridging the gap between the two colinear edges of physically defined boundaries. Stimuli which do not induce illusory contours, but reduce uncertainty about the spatial position of the line, give rise to a slight detection facilitation, but the (...) threshold of 75% correct responses is not attained. The data indicate that superimposing illusory contours and 1pixel thin subthreshold lines produces interactions which are similar to classic subthreshold summation. This provides psychophysical evidence for the functional equivalence of illusory and real lines, as suggested by neurophysiological data from single-cell recordings in V1 and V2 of cats and primates. (shrink)

This article introduces an experimental paradigm to selectively probe the multiple levels of visual processing that influence the formation of object contours, perceptual boundaries, and illusory contours. The experiments test the assumption that, to integrate contour information across space and contrast sign, a spatially short-range filtering process that is sensitive to contrast polarity inputs to a spatially long-range grouping process that pools signals from opposite contrast polarities. The stimuli consisted of thin subthreshold lines, flashed upon gaps between collinear inducers (...) which potentially enable the formation of illusory contours. The subthreshold lines were composed of one or more segments with opposite contrast polarities. The polarity nearest to the inducers was varied to differentially excite the short-range filtering process. The experimental results are consistent with neurophysiological evidence for cortical mechanisms of contour processing and with the Boundary Contour System model, which identifies the short-range filtering process with cortical simple cells, and the long-range grouping process with cortical bipole cells. (shrink)

Neuronal activities have recently been reported to exhibit power-law scaling behavior. However, it has not been demonstrated that the power-law component can play an important role in human perceptual functions. Here, we demonstrate that the power spectrum of magnetoencephalograph recordings of brain activity varies in coordination with perception of subthreshold visual stimuli. We observed that perceptual performance could be better explained by modulation of the power-law component than by modulation of the peak power in particular narrow frequency ranges. The (...) results suggest that the brain operates in a state of self-organized criticality, modulating the power spectral exponent of its activity to optimize its internal state for response to external stimuli. (shrink)

Cranial electrotherapy stimulation is a neuromodulation tool used for treating several clinical disorders, including insomnia, anxiety, and depression. More recently, a limited number of studies have examined CES for altering affect, physiology, and behavior in healthy, non-clinical samples. The physiological, neurochemical, and metabolic mechanisms underlying CES effects are currently unknown. Computational modeling suggests that electrical current administered with CES at the earlobes can reach cortical and subcortical regions at very low intensities associated with subthreshold neuromodulatory effects, and studies using (...) electroencephalography and functional magnetic resonance imaging show some effects on alpha band EEG activity, and modulation of the default mode network during CES administration. One theory suggests that CES modulates brain stem, limbic, and cortical regions and increases relative parasympathetic to sympathetic drive in the autonomic nervous system. There is no direct evidence supporting this theory, but one of its assumptions is that CES may induce its effects by stimulating afferent projections of the vagus nerve, which provides parasympathetic signals to the cardiorespiratory and digestive systems. In our critical review of studies using CES in clinical and non-clinical populations, we found severe methodological concerns, including potential conflicts of interest, risk of methodological and analytic biases, issues with sham credibility, lack of blinding, and a severe heterogeneity of CES parameters selected and employed across scientists, laboratories, institutions, and studies. These limitations make it difficult to derive consistent or compelling insights from the extant literature, tempering enthusiasm for CES and its potential to alter nervous system activity or behavior in meaningful or reliable ways. The lack of compelling evidence also motivates well-designed and relatively high-powered experiments to assess how CES might modulate the physiological, affective, and cognitive responses to stress. Establishing reliable empirical links between CES administration and human performance is critical for supporting its prospective use during occupational training, operations, or recovery, ensuring reliability and robustness of effects, characterizing if, when, and in whom such effects might arise, and ensuring that any benefits of CES outweigh the risks of adverse events. (shrink)

Using a classical conditioning technique, this study investigated whether nonconscious associative learning could be indexed by event-related brain activity . There were three phases. In a preconditioning baseline phase, pleasant and unpleasant facial schematics were presented in awareness . A conditioning phase followed, in which stimuli were presented outside awareness , with an unpleasant face linked to an aversive shock and a pleasant face not linked to a shock. The third, postconditioning phase, involved stimulus presentations in awareness . Evidence for (...) acquisition of a conditional response was sought by comparing suprathreshold pre- and postconditioning phases, as well as in the subthreshold conditioning phase itself. For the pre-postconditioning phase analyses, significant ERP component differences differentiating CS+ and CS− were observed for N1, P2, and especially P3. For the conditioning phase, significant differences were observed in the 100–400 ms. post-stimulus region reflecting a CS+ processing negativity. Brain activity does indeed index the acquisition of a conditional response to subthreshold stimuli. Associative learning can occur outside awareness. (shrink)

Using a classical conditioning technique, this study investigated whether nonconscious associative learning could be indexed by event-related brain activity . There were three phases. In a preconditioning baseline phase, pleasant and unpleasant facial schematics were presented in awareness . A conditioning phase followed, in which stimuli were presented outside awareness , with an unpleasant face linked to an aversive shock and a pleasant face not linked to a shock. The third, postconditioning phase, involved stimulus presentations in awareness . Evidence for (...) acquisition of a conditional response was sought by comparing suprathreshold pre- and postconditioning phases, as well as in the subthreshold conditioning phase itself. For the pre-postconditioning phase analyses, significant ERP component differences differentiating CS+ and CS− were observed for N1, P2, and especially P3. For the conditioning phase, significant differences were observed in the 100–400 ms. post-stimulus region reflecting a CS+ processing negativity. Brain activity does indeed index the acquisition of a conditional response to subthreshold stimuli. Associative learning can occur outside awareness. (shrink)

In the present study, we have demonstrated hysteresis phenomena in the excitability of single, enzymatically dissociated guinea pig ventricular myocytes. Membrane potentials were recorded with patch pipettes in the whole-cell current clamp configuration. Repetitive stimulation with depolarizing current pulses of constant cycle length and duration but varying strength led to predictable excitation (1:l) and non-excitation (1:0) patterns depending on current strength. In addition, transition between patterns depended on the direction of current intensity change and stable hysteresis loops were obtained in (...) stimulus:response pattern vs. current intensity plots in 14 cells. Increase of pulse duration and decrease of stimulation rate contributed to a reduction in hysteresis loop areas. Changes in amplitude and shape of the subthreshold responses during the transitions from one stable pattern to the other, suggested that activity led to an increase in membrane resistance, particularly in the voltage domain between resting potential, and threshold. Therefore, we modelled the dynamic behaviour of the single cells as a function of diastolic membrane resistance, using previously published analytical solutions. Numerical iteration of the analytical model equations closely reproduced the experimental hysteresis loops in both qualitative and quantitative ways. In particular, the effect of stimulation frequency on the model was similar to the experimental findings. The overall study suggests that the excitability pattern of guinea pig ventricular myocytes accounts for hysteresis and bistabilities when current intensity is allowed to fluctuate around threshold levels. (shrink)

We focus on the functional specificity of theta and alpha oscillations and show that theta is related to working memory, whereas alpha is related to semantic long-term memory. Recent studies, however, indicate that alpha oscillations also play an important role during short-term memory retention and retrieval. This latter finding provides support for the basic hypothesis suggested by Ruchkin et al.

Understanding spoken words involves a rapid mapping from speech to conceptual representations. One distributed feature-based conceptual account assumes that the statistical characteristics of concepts’ features—the number of concepts they occur in and likelihood of co-occurrence —determine conceptual activation. To test these claims, we investigated the role of distinctiveness/sharedness and correlational strength in speech-to-meaning mapping, using a lexical decision task and computational simulations. Responses were faster for concepts with higher sharedness, suggesting that shared features are facilitatory in tasks like lexical (...) decision that require access to them. Correlational strength facilitated responses for slower participants, suggesting a time-sensitive co-occurrence-driven settling mechanism. The computational simulation showed similar effects, with early effects of shared features and later effects of correlational strength. These results support a general-to-specific account of conceptual processing, whereby early activation of shared features is followed by the gradual emergence of a specific target representation. (shrink)

Goal‐directed cognition is often discussed in terms of specialized memory structures like the “goal stack.” The goal‐activation model presented here analyzes goal‐directed cognition in terms of the general memory constructs of activation and associative priming. The model embodies three predictive constraints: (1) the interference level, which arises from residual memory for old goals; (1) the strengthening constraint, which makes predictions about time to encode a new goal; and (3) the priming constraint, which makes predictions about the role of (...) cues in retrieving pending goals. These constraints are formulated algebraically and tested through simulation of latency and error data from the Tower of Hanoi, a means‐ends puzzle that depends heavily on suspension and resumption of goals. Implications of the model for understanding intention superiority, postcompletion error, and effects of task interruption are discussed. (shrink)

Considerable research has demonstrated that teachers’ self-efficacy plays a major role in implementing instructional practices in classroom lessons. Only few studies, however, have examined the interplay between how teachers’ self-efficacy and the challenges that lie outside their influence are related to their implementation of cognitive-activation strategies (CAS), especially in science classrooms. Using the Trends in Mathematics and Science Study (TIMSS) 2015 data from Grades 4, 5, 8, and 9, we explored the extent to which teachers’ self-efficacy in teaching science (...) and the perceived time constraints explained variation in the enactment of general and inquiry-based CAS. Overall, the findings revealed that highly self-efficacious teachers reported more frequent implementation of both general and inquiry-based CAS, whereas those who perceived strong time constraints reported a less frequent use of inquiry-based CAS. We further found that these relations differed significantly between primary- and secondary-school teachers and discuss these findings in light of teachers’ professional competences and the resources for science activities in primary and secondary education. We point to the theoretical implications of this study for enhancing the conceptual understanding of generic and specific aspects of CAS and the practical implications for teacher education, professional development, and educational policy. (shrink)