Biomedical Engineering Reference
In-Depth Information
Areas with greater fMRI response to the frame pair at the
240-ms ISI than to that at the 50-ms ISI were found only in the
ventral occipitotemporal region (
Fig. 11.8
). Areas with greater
response to the frame pair at the 0-ms ISI than to that at the
50-ms ISI were detected in the fusiform gyrus, the frontal cortex
and the parietal cortex. FG1 is the local maximum area in the
occipototemporal region that showed a greater response to the
frame pair at the 240-ms ISI than to that at the 50-ms ISI. FG2 is
the area that showed greater responses to the frame pairs at the 0-
ms and 240-ms ISI's than to that at the 50-ms ISI. FG3 is the area
that showed a greater response to the frame pair at the 0-ms ISI
than to that at the 50-ms ISI (How about the comparison with
240-ms?). The area FG2, located at the posterior fusiform gyrus,
was the only area that showed a significantly smaller response to
the frame pair at the 50-ms ISI than to those at the 0-msand
240-ms ISI's. The reduction of the fMRI response in this area
was paralleled by a reduction of visibility in our behavioral data
where all participants reported that both frames were visible as
separate frames at the 0-ms and 240-ms ISI's, but that the first
frame was invisible at the 50-ms ISI.
Figure 11.4
shows the
timecourses from this area. In the primary visual area V1, there
was no significant difference among responses to the frame pairs
at the ISI's of 0, 50- and 240-ms.
The responses in those occipitotemporal areas showed some
trends that depended on ISI (
Fig. 11.8
). The response to the
frame pair at the 0-ms ISI did not decrease from V1 to FG3,
while the responses to the frame pairs at the 50-ms and 240-ms
ISI's did decrease from V1 to FG3. In addition, there were dif-
ferences between the pattern of response reduction at the 50-ms
ISI and that at the 240-ms ISI. The response to the frame pair at
the 50-ms ISI decreased progressively from V1 to FG3, while the
response to the frame pair at the 240-ms ISI did not decrease
from V1 to FG2, but abruptly decreased from FG2 to FG3.
Although there was near loss of visibility of the small frame at
50-ms ISI, the relatively constant responses among 0-ms, 50-ms
and 240-ms ISI's in the primary visual area indicate that there
were neuronal activities in V1 corresponding to the first frame
as well as to the second frame at 50-ms ISI. The two frames
were presented in spatially separated positions on the display.
In spite of the very low visibility of the small frame, the inputs
related to the two frames did reach V1 at 50-ms ISI as much
as at 0-ms and 240-ms ISI where the visibility was clear. It
does indicate that the perception of the frame visibility does not
occur at V1.
In areas of FG1 and FG2, the 240-ms ISI did not induce
fMRI signal reduction for the paired stimuli but at 50-ms ISI,
the fMRI responses showed reduction. The interaction between
the two activities induced by the two stimuli was very short lived
