Odor-induced sound localization bias under unilateral intranasal trigeminal stimulation.

As a stereo odor cue, internostril odor influx could help us in many spatial tasks, including localization and navigation. Studies have also revealed that this benefit could be modulated by the asymmetric concentrations of both influxes (left nose vs right nose). The interaction between olfaction and vision, such as in object recognition and visual direction judgment, has been documented; however, little has been revealed about the impact of odor cues on sound localization. Here we adopted the ventriloquist paradigm in auditory-odor interactions and investigated sound localization with the concurrent unilateral odor influx. Specifically, we teased apart both the "nature" of the odors (pure olfactory stimulus vs. mixed olfactory/trigeminal stimulus) and the location of influx (left nose vs. right nose) and examined sound localization with the method of constant stimuli. Forty-one participants, who passed the Chinese Smell Identification Test, perceived sounds with different azimuths (0°, 5°, 10°, and 20° unilaterally deflected from the sagittal plane by head-related transfer function) and performed sound localization (leftward or rightward) tasks under concurrent, different unilateral odor influxes (10% v/v phenylethyl alcohol, PEA, as pure olfactory stimulus, 1% m/v menthol as mixed olfactory/trigeminal stimulus, and propylene glycol as the control). Meanwhile, they reported confidence levels of the judgments. Results suggested that unilateral PEA influx did not affect human sound localization judgments. However, unilateral menthol influx systematically biased the perceived sound localization, shifting toward the odor source. Our study provides evidence that unilateral odor influx could bias perceived sound localization only when the odor activates the trigeminal nerves.

Small numerosity advantage for sequential enumeration on RSVP stimuli: an object individuation-based account.

Although there is a large literature demonstrating rapid and accurate enumeration of small sets of simultaneously presented items (i.e., subitizing), it is unclear whether this small numerosity advantage (SNA) can also manifest in sequential enumeration. The present study thus has two aims: to establish a robust processing advantage for small numerosities during sequential enumeration using a rapid serial visual presentation (RSVP) paradigm, and to examine the underlying mechanism for a SNA in sequential enumeration. The results indicate that a small set of items presented in fast sequences can be enumerated accurately with a high precision and a SOA (stimulus onset asynchrony)-sensitive capacity limit, essentially generalizing the large literature on small numerosity advantage from spatial domain to temporal domain. A resource competition hypothesis was proposed and confirmed in further experiments. Specifically, sequential enumeration and other cognitive process, such as visual working memory (VWM), compete for a shared resource of object individuation by which items are segregated as individual entities. These results implied that the limited resource of object individuation can be allocated within time windows of flexible temporal scales during simultaneous and sequential enumerations. Taken together, the present study calls for attention to the dynamic aspect of the enumeration process and highlights the pivotal role of object individuation in underlying a wide range of mental operations, such as enumeration and VWM.

The internal representation of temporal orienting: A temporal pulse-accumulation and attentional-gating-based account.

Timing can be processed explicitly or implicitly. Temporal orienting is a typical implicit timing through which we can anticipate and prepare an optimized response to forthcoming events. It is, however, not yet clear whether mechanisms such as temporal-pulse accumulation and attentional gating (more attention, more accumulated temporal pulses) underly the internal representations of temporal orienting, as in explicit timing. To clarify this, a dual-task paradigm, consisting of a temporal orienting and an interference task, was adopted. Consistent with the temporal-pulse-accumulation and attentional-gating model, reaction times to the target detection of temporal orienting increased as the interference stimuli were temporally closer to the target, i.e., a location effect for temporal orienting. This effect is likely due to attention being diverted away from temporal orienting to monitor the occurrence of the interference stimuli for a longer time, resulting in greater temporal pulse loss and less accurate temporal orienting for conditions with later interference stimuli. The temporal-pulse-accumulation aspect in temporal orienting received further support by taking an explicit duration reproduction (containing a second temporal-pulse accumulation) as the interference task. On the one hand, temporal orienting became less accurate with increased temporal-pulse-accumulation overlaps between the dual tasks; on the other hand, two-way (one for temporal orienting and the other for duration reproduction), rather than one-way, location effects were observed, implying processing conflicts between the two temporal-pulse accumulations. Taken together, these results suggest that implicit and explicit timing may share common mechanisms upon internal temporal representations.

Perceived shift of the centres of contracting and expanding optic flow fields: Different biases in the lower-right and upper-right visual quadrants.

We studied differences in localizing the centres of flow in radially expanding and contracting patterns in different regions of the visual field. Our results suggest that the perceived centre of a peripherally viewed expanding pattern is shifted towards the fovea relative to that of a contracting pattern, but only in the lower right and upper right visual quadrants and when a single speed gradient with appropriate overall speeds of the trajectories of the moving dots was used. The biases were not systematically related to differences of sensitivity to optic flow in different quadrants. Further experiments demonstrated that the biases were likely due to a combination of two effects: an advantage of global processing in favor of the lower visual hemifield and a hemispheric asymmetry in attentional allocation in favor of motion-induced spatial displacement in the right visual hemifield. The bias in the lower right visual quadrant was speed gradient-sensitive and could be reduced to a non-significant level with the usage of multiple speed gradients, possibly due to a special role of the lower visual hemifield in extracting global information from the multiple speed gradients. A holistic processing on multiple speed gradients, rather than a predominant processing on a single speed gradient, was likely adopted. In contrast, the perceived bias in the upper right visual quadrant was overall speed-sensitive and could be reduced to a non-significant level with the reduction of the overall speeds of the trajectories. The implications of these results for understanding motion-induced spatial illusions are discussed.