时间和空间特征是感觉信息的两个基本属性。人类对时间和空间信息的视听加工已经得到了广泛的研究，但是在嗅觉模态中的研究还存在很多争议。一般认为，人类嗅知觉的时间分辨率受制于呼吸周期，空间分辨率则取决于头部在运动中对环境的采样。鼻两侧输入的差异能否提供嗅觉方位线索，嗅觉方位线索是否以及如何参与到空间导航中仍不清楚。本文通过两项研究分别探讨了人类嗅知觉在时间和空间维度的加工性质，分述如下：
（1）研究一中，我们设计了一个装置以精确锁定气味呈现相较于吸气起始的相位，这使得我们得以在一次吸气内操纵两种不同气味呈现的时间顺序和间隔，并要求被试分辨两次吸气间闻到的气味是否相同。数据显示两个气味间隔时差低至40 ms 时，人类被试就表现出了对它们呈现顺序是否一致的分辨能力，分辨正确率随气味间隔时差的增加而提升。这种分辨不是基于两种气味摩尔比例的差异，被试也并不能高于随机水平报告到底哪一种气味先呈现。这些行为结果证实人类嗅知觉对一次吸气内的时间信息敏感，提示气味引发的反应相对吸气的相位信息对嗅觉客体编码有显著贡献。
（2）研究二结合了对鼻两侧非三叉刺激性气味浓度差的操控和基于视觉光流的自身运动方向判断任务。心理物理测试显示鼻两侧气味浓度的适度差异会使被试的自身运动方向感知偏向于浓度较高的一侧，尽管他们无法报告哪侧鼻腔闻到的气味更强。进一步的，嗅觉方位信息依赖于鼻两侧的气味浓度比例关系而非数值差异，遵循费希纳定律，这种比例关系在知觉上表现为鼻两侧气味的主观强度差。颅内脑电数据显示静息状态下海马在吸气后的神经活动受鼻两侧气味浓度的左右关系的调制，表现为高浓度气味呈现一侧theta 和alpha 频段能量的降低，提示海马参与嗅觉方位的加工。此外，海马表现出对光流的特异性反应，其活动受到光流角度大小的调制，也有受嗅视方位一致性调节的趋势。这些结果证实了人类拥有立体嗅知觉，并可利用立体嗅觉进行空间导航。
综上，研究一发现人类嗅知觉有几十毫秒量级的时间敏感度，而研究二显示两侧鼻腔输入的差异可以提供方位线索并指引空间导航。这些发现拓展了我们对于人类嗅知觉的认识和理解。
其他摘要
Time and space are two fundamental aspects of human perception. Temporal and spatial processing are well-characterized in vision and audition yet remain largely unexplored in human olfaction. It is generally held that the temporal resolution of human olfactory perception is bounded by sniffing frequency, whereas the spatial resolution is determined by the sampling of environment during head/body movement. Whether inter-nostril differences in a single sniff provide any directional cue that contributes to spatial navigation has been controversial. Here two studies are presented that respectively address temporal and spatial processing in human olfactory perception:
(1) Study I examined whether the temporal order of events within a sniff influences the perceptual “snapshot” (outcome). We devised an apparatus that enabled us to phase-lock odor delivery to sniff onset and precisely manipulate onset asynchronies of odorants in humans. Psychophysical testing showed that participants were able to tell apart two odorants presented in the same or different order when the onset asynchrony was as low as 40 milliseconds. The performance improved with longer onset asynchronies and was not based on the molar ratio difference of the two odorants. Meanwhile, they were consistently at chance in reporting which odorant arrived first. These results provided behavioral evidence that human olfaction is sensitive to temporal patterns within a single sniff and indicated that timing of odor-evoked responses in relation to the sniff contributes to the perceived odor quality.
(2) Study II combined dichorhinic presentation of non-trigeminal odorants and optic flow that captures the pattern of apparent motion of surface elements in a visual scene. We demonstrated through formal psychophysical testing that a moderate binaural concentration disparity of a non-trigeminal odorant consistently biased recipients’perceived direction of self-motion toward the higher concentration side, despite that they could not verbalize which nostril smelled a stronger odor. We further showed that the effect depended on the internostril ratio of odor concentrations and not the numeric difference in concentration between the two nostrils. According to Fechner’s law, internostril concentration ratio is roughly equivalent to binaral disparity in perceived odor intensity. Using stereotactic electroencephalography, we further found that hippocampal activities at rest were modulated by the left-right relationship in odor concentration, exhibiting a decrease in theta and alpha power on the side with a higher odor concentration, which suggested that the hippocampus is involved in the processing of olfactory spatial information. In addition, the hippocampus responded strongly to optic flow, with response amplitude significantly modulated by the size of heading angle and marginally modulated by the congruency between olfactory and visual directional information. Taken together, these findings provided behavioral evidence that humans smell in stereo and subconsciously utilize stereo olfactory cues in spatial navigation.
In summary, study 1 found that human olfactory perception has a fine sensitivity to temporal information in tens of milliseconds, while study 2 showed that differences in nasal input from the two nostrils provided directional cues and guided spatial navigation. These findings have expanded our knowledge and understanding of human olfactory perception.
修改评论