color for middle values (if odd number of levels).
neutral.color.ramp
second color used when calling colorRamp
with low.color and high.color to define the color palettes.
colors
vector specifying the colors to use. This must be equal to
the number of likert levels.
plot.percent.low
whether to plot low percentages.
plot.percent.high
whether to plot high percentages.
plot.percent.neutral
whether to plot netural percentages.
plot.percents
whether to label each category/bar.
text.size
size of text attributes.
text.color
color of text attributes.
centered
if true, the bar plot will be centered around zero such that
the lower half of levels will be negative.
center
specifies which level should be treated as the center. For example,
center = 3 would use the third level as the center whereas
center = 3.5 would indicate no specific level is the center but
<= 3 are low levels and >= 4 are high levels (i.e. used for forced choice
items or those without a neutral option). This also influences where the
color breaks from low to high.
include.center
if TRUE, include the center level in the plot otherwise
the center will be excluded.
ordered
reorder items from high to low.
wrap
width to wrap label text for item labels
wrap.grouping
width to wrap label text for group labels.
legend
title for the legend.
legend.position
the position for the legend ("left", "right", "bottom",
"top", or two-element numeric vector).
panel.arrange
how panels for grouped likert items should be arrange.
Possible values are v (vertical, the default), h
(horizontal), and NULL (auto fill horizontal and vertical)
panel.strip.color
the background color for panel labels.
group.order
the order in which groups (for grouped items) or items
(for non-grouped items) should be plotted.
providing 
.