Collinear Motion Strengthens Local Context in Visual Detection.

Detection of elongated objects in the visual scene can be improved by additional elements flanking the object on the collinear axis. This is the collinear context effect (CE) and is represented in the long-range horizontal connection plexus in V1. The aim of this study was to test whether the visual collinear motion can improve the CE. In the three experiments of this study, the flank was presented with different types of motion. In particular, the collinear motion aligned with the longitudinal axis of the to-be-detected object: toward or away from it, and the orthogonal motion with a direction perpendicular to the collinear axis. Only collinear motion toward the target showed a robust and replicable empowerment of the CE. This dynamic modulation of the CE likely is implemented in the long-range horizontal connection plexus in V1, but, given that in addition it conveys the time information of motion, there must be a direct feedback in V1 from higher visual areas where motion perception is implemented, such as Middle Temporal (MT). Elongated visual objects moving along their longitudinal axis favor a propagation of activation in front of them via a network of interconnected units that allows the visual system to predict future positions of relevant items in the visual scene.

Electrophysiological Modulation in an Effort to Complete Illusory Figures: Configuration, Illusory Contour and Closure Effects.

Figure recognition process: From the coarse configuration standing from the background to the closure of a meaningful shape, was investigated by ERP technique. ERP components at different latencies from stimulus onset allowed to tap into the figure recognition process at discrete time-points when different cognitive operations take place. In this study, we present two experiments where the support-ratio (SR) of illusory figures was manipulated to vary continuously the recognition of geometrical figures. In the first experiment three shapes were used to vary the SR and the P1 component (80-130 ms) was modulated by the configuration-effect explained, in part for the first time, with the unbalanced physical stimulation between upper and lower visual field. In the second experiment, we used one shape and varied systematically the SR in a discrimination task. The N1 (130-180 ms) and the N2 (230-270 ms) were modulated by two effects: The Ic-effect, represented by the N1, and the closure-effect, represented by the N2, being larger when the SR was small and the discrimination more difficult with respect to large SRs and easier discrimination. These results showed that figure recognition proceeded from the coarse parsing of the visual scene (configuration-effect), through the completion of a set of illusory borders (Ic-effect) to the final assembling of a meaningful shape (closure-effect).

New ERP Methods Tailored Onto Single Subject Neuroanatomical Variability.

Gebodh and coworkers present an innovative method for strengthening the reliability with which event-related potential (ERP) components are recorded. By tailoring the experimental design to the neuroanatomical singularity of each observer, this method provides more robust and cleaner data.

Vigorous orientation signal propagates best from collinear motion.

In the present study, the Poggendorff illusion was tested with four types of stimuli: A moving dot, a moving bar parallel to the inducing lines, a moving bar collinear to the motion trajectory, and static bars as in the classic illusion. Psychometric functions of the alignment task showed that the collinear bar, where orientation and motion trajectory matched, yielded the best alignment performance almost eliminating the illusion; the vertical bar, on the contrary, showed the worst alignment, finally the dot and the static bars led to intermediate alignments. These results demonstrate the interaction between orientation and motion trajectory that likely takes place in the primary visual cortex (V1) where these two signals might be modulated by top-down activity from higher order areas such as the middle temporal (MT). This vigorous orientation-motion trajectory interaction allows extremely accurate positional predictions of moving objects in the visual scene, in particular during occlusion.

Unconscious priming by illusory figures: the role of the salient region.

In this study we provide evidence that unconscious priming can be obtained as a result of the processing of the salient region (SR) of illusory figures and without that of illusory contours (ICs). We used a metacontrast masking paradigm where illusory figures were masked by real figures. In Experiment 1 we found a clear priming effect when participants were asked to discriminate between square and diamond masks preceded by congruent or incongruent illusory square or diamond primes. It is likely that metacontrast impairs the processing of ICs but not of the SR; therefore the above result strongly suggests that the priming effect was specifically related to the processing of the SR. In Experiment 2 participants were tested in the same task as in Experiment 1 with additional primes in which the inducers were presented in the same locations but their shapes were changed so as to modify the global configuration. We termed these primes High, Low, and No Salient Region (HSR, LSR, and NSR, respectively). The HSR condition replicated Experiment 1, whereas in the LSR and NSR conditions the priming effect got progressively smaller. The results of Experiment 1 were replicated with the priming effect significantly larger in the HSR than in all other conditions. It was also larger in the HSR than in LSR condition and smallest but still present in the NSR condition. Taken together, these results indicate that the unconscious processing of only the SR yields a priming effect and that a reduction of the saliency of the SR leads to a reduction of the priming effect, while its elimination does not abolish it.

Interhemispheric transfer of spatial and semantic information: electrophysiological evidence.

The goal of this study was to cast light on the existence of functional callosal channels for the interhemispheric transfer (IHT) of spatial and semantic information. To do so, we recorded event-related potentials in healthy humans while performing a primed odd-even discrimination task. Targets were visually presented numbers preceded by single-letter primes signaling the probable presentation of an odd or an even number. Primes and targets could appear either in the same or in different visual fields, thus requiring an IHT in the latter case. The P1 and N2 components were influenced by IHT of spatial information only, whereas the later N400 was influenced by IHT of both spatial and semantic information. This was not the case for the P3b, which was modulated by semantic validity only. These results provide novel evidence of the existence of a temporally separated interhemispheric exchange of spatial and semantic information.

Does subliminal visual perception have an error-monitoring system?

There is substantial evidence that subliminal stimuli, i.e. stimuli that cannot be perceived consciously, may influence visually guided human behaviour. Two important points require further investigation, namely, the neural bases and the functional capability of unconscious stimulus processing. In this study we aimed at studying one specific aspect of the latter question, i.e. whether unconscious vision can feed into an error-monitoring system in much the same way as conscious vision. We therefore tested whether the event-related potential component known as error-related negativity, which represents the electrophysiological correlate of an error-monitoring system, is produced by unconscious errors. We found an error-related negativity not only for errors committed in a discrimination task with visible stimuli but also for those committed with subthreshold stimuli. Moreover, behavioural analysis showed post-error slowing of reaction time for correct responses following unconscious as well as conscious errors. Thus, the present results provide both electrophysiological and behavioural evidence of an error-monitoring system operating even when stimuli cannot access consciousness.

Lateralized readiness potential elicited by undetected visual stimuli.

Visual stimuli undetected by normal subjects as a result of masking procedures can nonetheless activate response preparation in motor areas and yield a motor response. An unanswered question is whether the same holds for undetected subliminal stimuli that are not responded to. To answer this question, in this study normal subjects were tested on a simple visual reaction time task with stimuli above, at, or below the psychophysical threshold while the lateralized readiness potential (LRP), i.e. an electrophysiological correlate of premotor activation in the primary motor cortex, was computed. We found a reliable LRP not only for suprathreshold stimuli but also for subthreshold stimuli to which subjects did not respond. The main thrust of this study is that it provides evidence that activation of the motor cortex occurs even with subthreshold visual stimuli and without an overt response.

Reasons for substance use and vulnerability factors in patients with substance use disorder and anxiety or mood disorders.

This cross-sectional study examined the reasons for substance use and the presence of vulnerability factors such as substance sensitivity, sensation seeking, and symptoms related to the attention deficit hyperactivity disorder (ADHD) in patients with substance use disorder (SUD) and comorbid mood and anxiety disorders by using the Structured Clinical Interview for the Spectrum of Substance Use (SCI-SUBS), a novel instrument designed to explore the spectrum of substance use and its clinical correlates. Study participants included 61 patients with SUD and mood or anxiety disorder, and two comparison groups including 35 patients with SUD only and 50 controls not in treatment for mental disorders or SUD. We found that patients with co-morbid mood or anxiety disorder had significantly higher scores on the SCI-SUBS domains 'substance sensitivity' and 'self-medication' as compared to those with SUD only. Scores on 'sensation seeking' and 'ADHD' domains were similar between both groups of patients and higher than in controls. Patients with comorbid mood or anxiety disorders showed a higher sensitivity to substances and were more prone to self-medication than those with SUD only. These characteristics should be taken into account in the diagnostic assessment and in long-term treatment to decrease the risk of relapse.

Dual diagnosis and quality of life in patients in treatment for opioid dependence.

This study examined the relationship between quality of life (QOL) and dual diagnosis among patients in treatment for opioid dependence. The study sample includes 57 patients with opioid dependence alone (OD) and 41 with opioid dependence and a psychiatric axis-I disorder (DD), recruited in 2001 and 2004 at the Drug Addiction Services (SerT) of Bolzano and Pontedera (Italy). Participants were 73.5% males, with a mean age of 35.1 years (SD = 8.0). A comparison group of 45 healthy controls was also included. Assessments included a structured psychiatric interview (SCID) and a self-report quality of life assessment (WHOQOL-BREF). Patients with DD reported significantly (p < 0.05) poorer QOL in the physical and psychological domains as compared with patients with OD. Both groups of patients with and without DD showed significantly (p < 0.001) poorer QOL in the physical, psychological, and social domains with respect to healthy participants. The scores on the "relationship with environment" domain did not differ among OD, DD, and controls. The present study provides preliminary evidence that dual diagnosis is associated with poorer QOL and emphasizes the need to target treatment for the mental disorder concomitantly with the dependence problem in patients in treatment for opioid dependence.