  Purpose
  To determine the influence on the contrast sensitivity when the stimulus
contains a fixation target in two retinal locations, foveal and parafoveal.
  Methods
  Four young adults with 0.0 logMar acuity participated in this study. The
stimulus was based on vertical sinusoidal gratings masked by a circular (for
foveal area) or a ring (for parafoveal area). To increase the luminance
resolution of the display a bit-stealing technique was used. Four different
sets of stimuli were generated, two for exploring the foveal sensitivity and
two for the parafoveal area. The difference between the sets designed for the
same area was the presence, or absence, of a fixation target (a white cross) in
the centre of the stimulus. A modified staircase method was implemented.
  Results
  The results show a drop in the contrast sensitivity when the fixation target
was present on the stimulus for frequencies smaller than 4 cycles per degree.
  Conclusions
  The presence of fixation targets diminishes the contrast sensitivity for low
to mid frequencies over different concentric areas of the retina. This could be
due to the fixational eye movements, different patterns of eye movements were
found using an eye tracker. The relationship between the sensitivity in the
foveal area and the parafoveal agrees with those reported by other authors
using different designs confirming that the new stimulus design is suitable to
measure the contrast sensitivity outside the foveal area.
