Hashimoto A, Watanabe S, Inui K, Hoshiyama M, Murase S, Kakigi R
Department of Integrative Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan.
Neuroscience. 2006;137(4):1427-37. doi: 10.1016/j.neuroscience.2005.10.047. Epub 2005 Dec 9.
We recorded event-related magnetic fields following a target stimulus followed by a masking stimulus to investigate the visual backward masking effect using a helmet-type magnetoencephalography system in humans.
In the target stimulus with masking stimulus conditions, duration of the target stimulus was constant at 16 ms, and duration of the masking stimulus was altered (16, 48 and 144 ms). The target stimulus was masked by the 144-ms masking stimulus, but not by the 16-ms masking stimulus, and was obscured by the 48-ms masking stimulus. For control conditions (Single-condition), event-related magnetic fields were recorded following the sole presentation of the masking stimulus for 32, 64 or 160 ms.
One major response was obtained at 180 ms after the onset of the stimulation in each condition. The equivalent current dipole of one major response was estimated to lie in the occipital lobe, but there was a relatively large inter-individual difference. There was no significant difference in latency between the target stimulus with masking stimulus conditions and Single-conditions. In the target stimulus with masking stimulus conditions with the 48- and 144-ms masking stimulus, the root mean square value did not differ from that in the respective Single-condition, while the root mean square value for the target stimulus with masking stimulus conditions with the 16-ms masking stimulus was significantly smaller than that in the Single-condition with the 32-ms masking stimulus, but not different from that in the Single-condition with the 16-ms masking stimulus.
The peak latency of one major response depended on the onset of the first stimulus for both the target stimulus with masking stimulus conditions and Single-condition, but the root mean square value depended on the duration of the masking stimulus. We concluded that the temporal information for the target stimulus was preserved during the masking effect, while the figural information was interrupted by the masking stimulus. Our results suggested that temporal factors for the stimulus were processed differently from those responsible for the object's recognition during backward masking.
我们记录了在目标刺激后紧接着一个掩蔽刺激时的事件相关磁场，以使用头盔式脑磁图系统在人类中研究视觉后向掩蔽效应。
在目标刺激加掩蔽刺激条件下，目标刺激的持续时间恒定为16毫秒，掩蔽刺激的持续时间有所改变（16、48和144毫秒）。目标刺激被144毫秒的掩蔽刺激所掩蔽，但不被16毫秒的掩蔽刺激所掩蔽，并且被48毫秒的掩蔽刺激所遮挡。对于对照条件（单一条件），在仅呈现掩蔽刺激32、64或160毫秒后记录事件相关磁场。
在每种条件下，刺激开始后180毫秒获得了一个主要反应。一个主要反应的等效电流偶极估计位于枕叶，但个体间差异相对较大。目标刺激加掩蔽刺激条件与单一条件之间的潜伏期没有显著差异。在使用48毫秒和144毫秒掩蔽刺激的目标刺激加掩蔽刺激条件下，均方根值与各自单一条件下的均方根值没有差异，而使用16毫秒掩蔽刺激的目标刺激加掩蔽刺激条件下的均方根值显著小于使用32毫秒掩蔽刺激的单一条件下的均方根值，但与使用16毫秒掩蔽刺激的单一条件下的均方根值没有差异。
对于目标刺激加掩蔽刺激条件和单一条件，一个主要反应的峰值潜伏期取决于第一个刺激的开始，但均方根值取决于掩蔽刺激的持续时间。我们得出结论，在掩蔽效应期间目标刺激的时间信息得以保留，而图形信息被掩蔽刺激中断。我们的结果表明，在向后掩蔽过程中，刺激的时间因素与负责物体识别的因素处理方式不同。
