Intramodal and cross-modal perceptual grouping based on the spatial proximity and temporal closeness between multiple sensory stimuli, as an operational principle has built a coherent and meaningful representation of the multisensory event/object. To implement and investigate the cross-modal perceptual grouping, researchers have employed excellent paradigms of spatial/temporal ventriloquism and cross-modal dynamic capture and have revealed the conditional constraints as well as the functional facilitations among various correspondence of sensory properties, with featured behavioral evidence, computational framework as well as brain oscillation patterns. Typically, synesthetic correspondence as a special type of cross-modal correspondence can shape the efficiency and effect-size of cross-modal interaction. For example, factors such as pitch/loudness in the auditory dimension with size/brightness in the visual dimension could modulate the strength of the cross-modal temporal capture. The empirical behavioral findings, as well as psychophysical and neurophysiological evidence to address the cross-modal perceptual grouping and synesthetic correspondence, were summarized in this review. Finally, the potential applications (such as artificial synesthesia device) and how synesthetic correspondence interface with semantics (sensory linguistics), as well as the promising research questions in this field have been discussed.

Number-color synesthesia is a condition in which synesthetes perceive numbers with concurrent experience of specific, corresponding colors. It has been proposed that synesthetic association exists primarily between representations of Arabic digit graphemes and colors, and a secondary, semantic connection between numerosity and colors is built via repeated co-activation. However, this distinction between the graphemic and semantic pathways of synesthetic number-color connection has not been empirically tested. The current study aims to dissociate graphemic and semantic aspects of color activations in number-color synesthesia by comparing their time courses. We adopted a synesthetic priming paradigm with varied stimuli onset asynchronies (SOAs). A number (2-6, prime) was presented in one of three notations: digit, dice, or non-canonical dot pattern, and a color patch (target) appeared with an SOA of 0, 100, 300, 400, or 800 ms. Participants reported the color as quickly as possible. Using the congruency effect (i.e., shorter reaction time when target color matched the synesthetic color of number prime) as an index of synesthetic color activation level, we revealed that the effect from the graphemic pathway is quick and relatively persistent, while the effect from the semantic pathway unfolds at a later stage and is more transient. The dissociation between the graphemic and semantic pathways of synesthesia implies further functional distinction within \"conceptual synesthesia\", which has been originally discussed as a unitary phenomenon. This distinction has been demonstrated by the differential time courses of synesthetic color activations, and suggested that a presumed, single type of synesthesia could involve multiple mechanisms.

Consistent with the temporal ventriloquism effect, synesthetic correspondence between the features of visual size and auditory pitch has been shown to modulate the performance of visual temporal order judgment (TOJ) in typical adults. Here in the two main experiments we recruited seventeen dyslexic children and twenty typically developing children to perform a visual TOJ task and measured their ability of synesthetic correspondence between visual size and auditory pitch. In Experiment 1, participants were shown two consecutively presented visual discs that were temporally flanked by two synesthetic congruent or incongruent auditory beeps. In Experiment 2, participants received a crossmodal matching test (visual-size vs. auditory pitch). The results showed that compared to the typically developing group, dyslexic children benefited more from cross-modal synesthetic correspondence to partially compensate for their deficiency in visual TOJ task. The multisensory facilitation for timing performance was correlated with reading ability (Exp.1). Moreover, dyslexic children formed intact \"congruent\" matching of visually larger shapes to lower auditory pitch, and visually smaller shapes to higher auditory pitch, as did their typically developing peers (Exp 2). The results of our present study suggested general deficits of temporal processing in dyslexic children, However, with relatively intact ability of auditory pitch-visual size matching, dyslexic children could separate visual events using auditory cues. The current study also indicates a feasible way to improve the reading ability by exploiting temporal ventriloquism effect, modulated by appropriate crossmodal synesthetic associations.

BACKGROUND: The history of Chinese spices has received increasing attention in recent years, but little research been carried out on where they fit on the food-medicine continuum for early China, during the formation of the classical medical system. This paper describes how the synaesthetic qualities of spices attracted a particular analysis in that emerging system which serves to mark them as different to other medical materials and foodstuffs. We aim to clarify the special role created for spices to accommodate their boundary-crossing synaesthetic action on the body.
METHODS: This paper analyses the contents of several spice bags excavated in 1972 from a tomb that was closed in the second century BCE. It uses archaeological reports of material culture together with the early Chinese textual record, extant in both manuscripts and received texts, to bring out the role of spices in ritual, food and medicine.
RESULTS: Noting that the flavours and aromas of early China were assigned physiological potency in the first centuries BCE, we argue that by medieval times the unique synaesthetic role that spices played in mediating the senses was systematically medicalised. While being deployed for the purpose of curing disease in medicine, they also remained within the realm of everyday healthcare, and religious practice, deployed both as aromatics to perfume the environment, attracting benign spirits, but also to ward off the agents of disease, as well as for enhancing health through their use in cookery.
CONCLUSIONS: While foodstuffs entered the digestive system spices were all considered \'pungent\' in the emerging clasical medical system. They acted on the body through the nose and lungs, making them neither food nor drug. This implicit categorisation medicalised spices which, like music, could affect the passions and lighten the spirit, codifying observations about the impact on the body of the ritual environment.