Laterality differences and practice effects under central backward masking conditions

When two targets are presented in a rapid serial visual presentation (RSVP), recognition of the second target (T2) is usually reduced when presented 150-500 ms after the first target, demonstrating an attentional blink (AB). Previous studies have shown a left visual-field (LVF) advantage in T2 recognition, when T2 was embedded in one of two streams, demanding top-down attention for its recognition. Here, we explored the impact of bottom-up saliency on spatial asymmetry in the AB. When T2 was spatially shifted outside from the RSVP, creating an abrupt onset of T2, right T2s showed a right visual-field (RVF) advantage. In lag-1 trials, right T2s were not only better recognized, but also showed a low T1-T2 order error rate. In contrast, recognized left T2s exhibited high order error rate. Without abrupt onset, symmetrical AB was found and order error rate was similarly low in both sides. Follow-up experiments showed that, while RVF advantage was related to bottom-up saliency, order errors were affected by T1 mask. The discrepancy between LVF and RVF advantage in the AB could be resolved in terms of two mechanisms of attentional gating: top-down attentional gating, which is biased towards LVF, and bottom-up attentional gating, which is biased towards RVF.

The neural basis of the right visual field advantage in reading: An MEG analysis using virtual electrodes

In recognition of the ecological importance of processing the talking face and its potential role in the development of right hemisphere specialization for face processing, descriptive studies examined the effects of concurrent speech on hemispheric lateralization for face recognition. To explore the potentially special nature of the face-speech concurrence, the effect of speech on inverted face recognition was also examined. Separate groups of right-handed participants took part in each of 4 studies. In Study 1, participants were asked to identify which of 4 male faces was presented in tachistoscopic fashion via computer. Correct recognition of faces was significantly faster in the left visual field (LVF) than in the right visual field (RVF), and the majority of participants exhibited a LVF processing-speed advantage (ADV). However, those participants whose responses to faces were faster in the RVF (RVF ADV) were more accurate at recognizing faces. In Study 2, a spoken word was incidentally presented simultaneously with each face. This altered hemispheric lateralization for face recognition. There was no longer evidence for LVF responses being faster than RVF ones or for participants with a RVF ADV being better at recognizing faces. However, these participants were superior at an unannounced speech recognition test. Unexpectedly, concurrent processing did not diminish performance on face recognition. Good memory for the incidental speech was also evident during an unannounced speech recognition test, indicating that participants successfully did 2 things at once. It was hypothesized that the special nature of the face-speech combination was responsible for this. Concurrent processing of the nonecological combination of inverted faces and speech provided no evidence in support of this hypothesis.

The time needed to decide whether the second of two successively presented sinusoidal gratings was of a higher or lower spatial frequency than the first was measured for spatial frequencies of 1, 2, 4, 8, and 12 cycles per degree (cpd) presented in either the left visual field (LVF) or right visual field (RVF). A LVF advantage was found for discriminating within the low-spatial-frequency range (i.e., 1 and 2 cpd), whereas a RVF advantage was found for discriminating within the high-spatial-frequency range (i.e., 4-12 cpd). These findings support the conclusion that hemispheric asymmetries in the processing of gratings arise when comparisons are made between the output of spatial-frequency channels.

IntroductionThe current study investigated the influence of the number of meanings on visual word recognition, with a particular focus on hemispheric dynamics.MethodsBy reanalyzing parafoveal Korean lexical decision data, we examined how words with a high versus low number of meanings affect right visual field advantage (RVFA) and bilateral redundancy gain (BRG).ResultsThe words with a greater number of meanings exhibited a stronger RVFA and reduced BRG compared to words with fewer meanings.DiscussionThe findings suggest that the facilitatory effects associated with multiple meanings are more pronounced in the left hemisphere (LH) than in the right hemisphere (RH). Furthermore, the increased lateralization of processing within the LH appears to diminish the need for interhemispheric interactions, leading to decreased coordination between the hemispheres. These results imply that the number of meanings in words shapes interhemispheric dynamics during visual word recognition. The implications of these findings are discussed in relation to theoretical models of visual word recognition and hemispheric differences in language processing.

Locus of information in words and the right visual field effect

ABSTRACTIn lateralized lexical decision tasks (LDTs), accuracy is higher and reaction times (RTs) are faster for right visual field (RVF) than left visual field (LVF) presentations. Visual field differences are thought to demonstrate the left hemisphere's (LH) dominance for language. The use of different tasks and words between studies and languages make direct comparisons difficult. We performed a lateralized LDT for which we selected four to six letter words that are used in three languages of Switzerland (French, German, and Italian) and English and Dutch. We accounted for the potential moderating roles of sex, handedness and multilingualism (early acquisition versus late acquisition of at least one second language). One hundred participants were tested at a French-speaking University in Switzerland. All performed a French vocabulary knowledge task [Brysbaert (2013). Lextale_FR a fast, free, and efficient test to measure language proficiency in French. Psychologica Belgica, 53(1), 23–27. Retrieved from http://hdl.handle.net/1854/LU-4373981]. Results showed a RVF over LVF advantage (accuracy, RTs and signal detection theory measures) for all groups, that is, irrespective of participants’ sex, handedness and how many languages they spoke. We observed, however, that enhanced vocabulary knowledge related to a right hemisphere shift in early bilinguals and a LH shift in late bilinguals. We discuss how the current observations can inform future studies suitable for the validation of the current task using an “international” vocabulary.

Visual field asymmetries in attention vary with self-reported attention deficits

Purpose: Results from previous studies indicate that the magnitude of attention effects depends on stimulus features/task (e.g., Lee et al, 1997; Morrone et al, 2002). Here, we used a full/poor attention paradigm to investigate attention effects on two different stimuli/tasks: direction of motion and orientation discrimination. Data were obtained for central (CVF), left (LVF) and right visual field (RVF) to see if attention effects vary across space. Methods: On the motion task, subjects reported direction of a moving dot field (“left” vs. “right”). On the orientation task, subjects reported the tilt of a 0.8 cpd contrast grating (“clockwise” vs. “counterclockwise”). Stimuli subtended 5 degrees, and RVF and LVF stimuli were centered 5 degrees eccentric to fixation. Thresholds were obtained in two conditions: 1) Full Attention: Subjects performed a single-task, reporting direction (or orientation), and 2) Poor Attention: Subjects performed a dual-task, first counting the number of closed shapes at the fixation point, then reporting stimulus direction (or orientation). Attention effects were calculated as Thrpoor/Thrfull. Results: For orientation, attention effects were constant across space (LVF=1.29, CVF=1.45, RVF=1.20). However, for motion, attention effects varied across space (LVF=1.74, CVF=1.41, RVF=1.07; p=0.002). The difference between the LVF and RVF was driven by lower thresholds in the LVF under full attention (1.2-fold, p=0.045), yet higher thresholds in the LVF under poor attention (1.3-fold, p=0.006). Conclusions: The different attention effects for RVF vs. LVF motion suggest that attentional resources for motion may be enhanced in the RVF (perhaps from learning to read left-to-right, see Rayner 1998).

In spite of the excellent temporal resolution of event-related EEG potentials (ERPs), the overlapping potentials evoked by masked and masking stimuli are hard to disentangle. However, when both masked and masking stimuli consist of pairs of relevant and irrelevant stimuli, one left and one right from fixation, with the side of the relevant element varying between pairs, effects of masked and masking stimuli can be distinguished by means of the contralateral preponderance of the potentials evoked by the relevant elements, because the relevant elements may independently change sides in masked and masking stimuli. Based on a reanalysis of data from which only selected contralateral-ipsilateral effects had been previously published, the present contribution will provide a more complete picture of the ERP effects in a masked-priming task. Indeed, effects evoked by masked primes and masking targets heavily overlapped in conventional ERPs and could be disentangled to a certain degree by contralateral-ipsilateral differences. Their major component, the N2pc, is interpreted as indicating preferential processing of stimuli matching the target template, which process can neither be identified with conscious perception nor with shifts of spatial attention. The measurements showed that the triggering of response preparation by the masked stimuli did not depend on their discriminability, and their priming effects on the processing of the following target stimuli were qualitatively different for stimulus identification and for response preparation. These results provide another piece of evidence for the independence of motor-related and perception-related effects of masked stimuli.

Cross-language tests of hemispheric strategies in reading nonwords.

Visual prime stimuli can affect the processing of following target stimuli even if their visibility is reduced due to visual masking. Prime visibility depends on the stimulus parameters of the prime and those of the mask. Here we explored the effects of prime stimuli and modulated their visibility by continuous flash suppression (CFS). CFS reduces the visibility of a stimulus presented to one eye by simultaneously presenting a series of high-contrast masking stimuli to the other eye. We manipulated the strength of CFS effects on perception and examined how action priming effects of the masked stimuli varied under the same conditions. Prime visibility was modulated by the contrast of the primes (Experiments 1 and 2), the contrast of the masks (Experiments 2 and 3), and by the stimulus onset asynchrony between prime and target stimuli (all experiments). Surprisingly, action priming effects were modulated by these experimental variables in a parallel way. In addition, individual differences between participants in prime visibility correlated with individual differences in action priming. Our findings suggest that action priming and prime perception depend in similar ways on prime contrast, mask contrast, stimulus onset asynchrony, and individual dispositions in CFS. These findings distinguish CFS from other perceptual suppression techniques, such as backward masking, that allow reducing prime visibility without parallel effects on action priming. Our results corroborate the view that CFS interferes with visual processing at early stages in the cortical hierarchy with similar effects on later processing for perception and action.

Observers are faster to detect a target among a set of distracters if the targets and distracters come from different color categories. This cross-boundary advantage seems to be limited to the right visual field, which is consistent with the dominance of the left hemisphere for language processing [Gilbert et al., Proc. Natl. Acad. Sci. USA 103, 489 (2006)]. Here we study whether a similar visual field advantage is found in the color identification task in speakers of Mandarin, a language that uses a logographic system. Forty late Mandarin-English bilinguals performed a blue-green color categorization task, in a blocked design, in their first language (L1: Mandarin) or second language (L2: English). Eleven color singletons ranging from blue to green were presented for 160 ms, randomly in the left visual field (LVF) or right visual field (RVF). Color boundary and reaction times (RTs) at the color boundary were estimated in L1 and L2, for both visual fields. We found that the color boundary did not differ between the languages; RTs at the color boundary, however, were on average more than 100 ms shorter in the English compared to the Mandarin sessions, but only when the stimuli were presented in the RVF. The finding may be explained by the script nature of the two languages: Mandarin logographic characters are analyzed visuospatially in the right hemisphere, which conceivably facilitates identification of color presented to the LVF.

A partial report procedure and a backward masking paradigm were employed to explore lateral asymmetries in components of letter recognition. Stimulus displays were displaced off-centre into the left visual field (LVF) or the right visual field (RVF). Visual field differences in the effect of a delayed backward mask indicated an RVF superiority in the rate of read-out or encoding. Comparison of masked and unmasked full report also yielded estimates of iconic persistence. The persistence of these peripheral displays was surprisingly brief, although it was significantly longer in the LVF (57 ms) than in the RVF (34 ms). Precueing by colour and by location produced a larger partial report advantage in the RVF, reflecting a superiority in selective sampling. With postcueing no partial report effect was obtained at any delay, and this failure was attributed to the briefness of the iconic persistence.

Visual masking occurs when the perception of a brief target stimulus is affected by a preceding or succeeding mask. The uncoupling of the target and its perception allows an opportunity to investigate the neuronal mechanisms involved in sensory representation and visual perception. To determine whether rats are a suitable model for subsequent studies of the neuronal basis of visual masking, we first demonstrated that decoding of neuronal responses recorded in the primary visual cortex (V1) of anaesthetized rats predicted that orientation discrimination performance should decline when masking stimuli are presented immediately before or after oriented target stimuli. We then trained Long-Evans rats (n = 7) to discriminate between horizontal and vertical target Gabors or gratings. In some trials, a plaid mask was presented at varying stimulus onset asynchronies (SOAs) relative to the target. Spatially, the masks were presented either overlapping or surrounding the target location. In the absence of a mask, all animals could reliably discriminate orientation when stimulus durations were 16 ms or longer. In the presence of a mask, discrimination performance was impaired, but did not systematically vary with SOA as is typical of visual masking. In humans performing a similar task, we found visual masking impaired perception of the target at short SOAs regardless of the spatial or temporal configuration of stimuli. Our findings indicate that visual masking may be difficult to observe in rats as the stimulus parameters necessary to quantify masking will make the task so difficult that it prevents robust measurement of psychophysical performance. Thus, our results suggest that rats may not be an ideal model to investigate the effects of visual masking on perception.