Capacity limitations of attentional resources allow only a fraction of sensory inputs to enter our awareness. Most prominently, in the attentional blink, the observer fails to detect the second of two rapidly successive targets that are presented in a sequence of distractor items. This study investigated whether phonological (in)congruency between visual target letters and spoken letters is modulated by subjects’ awareness. In a visual attentional blink paradigm, subjects were presented with two visual targets (buildings and capital Latin letters, respectively) in a sequence of rapidly presented distractor items. A beep was presented always with T1. We manipulated the presence/absence and phonological congruency of the spoken letter that was presented concurrently with T2. Subjects reported the identity of T1 and T2 and reported the visibility of T2. Behaviorally, subjects correctly identified T2 when it was reported to be either visible or unsure, while performances were below chance level when T2 was reported to be invisible. At the neural level, the anterior cingulate was activated for invisible > unsure > visible T2. In contrast, visible relative to invisible trials increased activation in bilateral cerebellum, pre/post-central gyri extending into parietal sulci and bilateral inferior occipital gyri. Incongruency effects were observed in the left inferior frontal gyrus, caudate nucleus and insula only for visible stimuli. In conclusion, phonological incongruency is processed differently when subjects are aware of the visual stimulus. This indicates that multisensory integration is not automatic but depends on subjects’ cognitive state.
The Red Sea Aphanius dispar and the Mediterranean Aphanius fasciatus can be found sympatrically in the Suez Canal, in the lakes of Lower Egypt, and along the Mediterranean coast of Israel. Both species are closely related and are known to form hybrids when held together. Putative hybrids of these species were found in the shallow Bardawil Lagoon on the northern coast of Sinai. The lagoon is unique in the eastern Mediterranean by being totally hypersaline without any brackish or freshwater sections. Samples were obtained using a small mesh-size experimental beach seine between April 1973 and March 1975. Among the 4,600 specimens of killifish examined, 45% belonged to A. dispar, 17% to A. fasciatus, and 38% to their putative hybrids. Seasonal abundance was similar in all three taxa; there were few fish during the winter months and from June to October, abundant fish, mostly juveniles, with peaking in July. Examination of gonads revealed that the reproductive period of the two species is from March to September when water temperatures varied between 21 and 33 °C. The hybrids had only rudimentary gonads. The size of A. dispar and the hybrid in the lagoon varied between 25 and 65 mm total length. A. fasciatus was smaller, not exceeding 35 mm, although in other regions it can reach 75 mm.
The role attention plays in our experience of a coherent, multisensory world is still controversial. On the one hand, a subset of inputs may be selected for detailed processing and multisensory integration in a top-down manner, i.e., guidance of multisensory integration by attention. On the other hand, stimuli may be integrated in a bottom-up fashion according to low-level properties such as spatial coincidence, thereby capturing attention. Moreover, attention itself is multifaceted and can be described via both top-down and bottom-up mechanisms. Thus, the interaction between attention and multisensory integration is complex and situation-dependent. The authors of this opinion paper are researchers who have contributed to this discussion from behavioural, computational and neurophysiological perspectives. We posed a series of questions, the goal of which was to illustrate the interplay between bottom-up and top-down processes in various multisensory scenarios in order to clarify the standpoint taken by each author and with the hope of reaching a consensus. Although divergence of viewpoint emerges in the current responses, there is also considerable overlap: In general, it can be concluded that the amount of influence that attention exerts on MSI depends on the current task as well as prior knowledge and expectations of the observer. Moreover stimulus properties such as the reliability and salience also determine how open the processing is to influences of attention.
The brain should integrate sensory inputs only when they emanate from a common source and segregate those from different sources. Sensory correspondences are important cues informing the brain whether two sensory inputs are generated by a common event and should hence be integrated. Most prominently, sensory inputs should co-occur in time and space. More complex audiovisual stimuli may also be congruent in terms of semantics (e.g., objects and source sounds) or phonology (e.g., spoken and written words; linked via common linguistic labels). Surprisingly, metaphoric relations (e.g., pitch and height) have also been shown to influence audiovisual integration. The neural mechanisms that mediate these metaphoric congruency effects are only poorly understood. They may be mediated via (i) natural multisensory binding, (ii) common linguistic labels or (iii) semantics. In this talk, we will present a series of studies that investigate whether these different types of audiovisual correspondences are processed by distinct neural systems. Further, we investigate how those systems are employed by metaphoric audiovisual correspondences. Our results demonstrate that different classes of audiovisual correspondences influence multisensory integration at distinct levels of the cortical hierarchy. Spatiotemporal incongruency is detected already at the primary cortical level. Natural (e.g., motion direction) and phonological incongruency influences MSI in areas involved in motion or phonological processing. Critically, metaphoric interactions emerge in neural systems that are shared with natural and semantic incongruency. This activation pattern may reflect the ambivalent nature of metaphoric audiovisual interactions relying on both natural and semantic correspondences.