A Real-Time and Portable Bionic Eye Simulator - Biomedical Engineering Systems and Technologies - page 43

Fig. 15. Maze Test: Mode vs. Average No. of Intercepted Balls

The number of intercepted balls for each of the non-control modes was significantly
shorter than the control mode ( p < 0 . 05 for all). There was also a significant difference
between the non-control modes themselves ( p < 0 . 05 for both 4Hz vs 10Hz, and 10Hz
vs 60Hz). The graph shows an upward trend in intercepted balls as the frame rate is
increased.

5.4 Discussion

The Maze Test results show that subjects take much longer to finish the test in any
of the non-control modes compared to the control, and that although the binary and
reduced frame rate modes took slightly longer to complete than the 4-level full frame
rate mode, the difference was not significant. This trend is also shown in the average
number of collisions, but the standard error is very large. From observations made while
building and testing the system, reduction in colour depth and frame rate does increase
the difficulty of most general tasks including navigational and obstacle avoidance tasks.
Possible reasons for this not being made clear in this particular test's results are that
the maze area was fairly small and straightforward so the task could be completed in a
relatively short amount of time, and the number of test subjects was low, presenting a
relatively large error. Also, the obstacles used in this test were large and obvious and
so subjects may not have benefited a lot from an increased colour depth and frame rate.
Another problem could be the order of the modes in which the subjects were tested was
made consistent and that the 'harder' modes were tested later. A learning effect just
from repeated testing, even with the changing obstacle placement and accommodation
time between tests, could cause a decrease in times for the later tested 'harder' modes
and hence reduce differences between them and the earlier test 'easier' modes.
For the Chessboard Test, the results demonstrate that the binary modes were signif-
icantly longer than the 4-level thresholding modes for each repeated test. The results
also show that there is a clear downwards trend with increasing number of tests for
both modes. The average number of mistakes also shows these trends, and that the bi-
nary has more mistakes than the 4-level and that both modes decrease over repeated
testing, however the standard error is very large. The reason the tests were completed
much faster on 4-level compared to binary is likely because this test is based primarily
on contrast discrimination and the extra levels of grey available on the 4-level allow
the subjects to be able to tell the difference between the dark and light chess pieces