The Use of Sensory Information 331Figure 12.11 Elliptical end-position distributions of movements from a
start position to concentrically arranged targets; circles mark the target areas
(after Gordon et al., 1994).
mentioned above, Nougier et al. (1996) found basically cor-
rect amplitude specifications in periodic movements between
two targets, although there were gross errors in the actual
end-positions relative to the targets.
Contrasting with the evidence for amplitude specifications
or relative reference systems in tasks of the type “reaching
from one object to another,” in tasks of the type “reaching out
for an object” there is evidence for a reference system that is
fixed, with the origin being at the shoulder or at a location in-
termediate between head and shoulder (Flanders, Helms
Tillery, & Soechting, 1992). The analyses that led to this con-
clusion were again based on the assumption that errors of am-
plitude and direction should be essentially independent.
However, when the start position of the hand is varied, an in-
fluence can again be seen, but not as dominant an influence as
in the task of Gordon et al. (1994). Thus, McIntyre, Stratta,
and Lacquaniti (1998) concluded that there is a mixture
of different reference systems; in addition, errors of visual
localization are added to errors of pointing.
Taken together, the evidence suggests that target infor-
mation in general is specified both in terms of (egocentric)
positions and in terms of (allocentric) distances and direc-
tions. Localization in terms of egocentric positions requires
that, to perform a movement, the visual reference system
be transformed to a proprioceptive-motor reference system,
the first having its origin at the cyclopean eye, the latter hav-
ing its origin at the shoulder, at least for certain types of arm
movements. Localization in terms of allocentric distances
and directions requires that the visual reference system be
aligned with the proprioceptive-motor reference system in a
way that the origin is in the current position of the end-
effector. The relative importance of the two reference sys-
tems depends on task characteristics. In addition, there is
also evidence that it can be modulated intentionally
(Abrams & Landgraf, 1990).
Although spatial targets are mostly specified visually, they
can also be specified proprioceptively, and again there is evi-
dence for target specifications in terms of both position and
amplitude, with the relative importance of these being af-
fected both by task characteristics and intentions. In these ex-
periments, participants produce a movement to a mechanical
stop and thereafter reproduce this movement. When the start
position is different for the second movement, participants
can be instructed to reproduce either the amplitude of the first
movement or its end-position. The general finding is a bias
toward the target amplitude when the task is to reproduce the
end-position, and a bias toward the end-position when the
task is to reproduce the amplitude (Laabs, 1974). Although
typically the reproduction of the end-position is more accu-
rate than the reproduction of the amplitude, this is more so for
longer movements, less so for shorter ones, and it may even
be reversed for very short ones (Gundry, 1975; Stelmach,
Kelso, & Wallace, 1975).Specification of Temporal TargetsIn tasks like catching, precisely timed movements are re-
quired: The hand must be in the proper place at the proper
time and be closed with the proper timing to hold the ball. In
very simple experimental tasks, finger taps have to be syn-
chronized with pacing tones. Although the specification of
temporal targets is fairly trivial in such tasks, the findings re-
veal to which aspects of the movements temporal goals are
related. A characteristic finding is negative asynchrony, a sys-
tematic lead of the taps in the range of 20–50 ms, which, for
example, is longer for tapping with the foot than for tapping
with the finger (e.g., Aschersleben & Prinz, 1995).
The negative asynchrony is taken to indicate that the tem-
poral target is not related to the physical movement itself, but
rather to its sensory consequences, proprioceptive and tactile
ones in particular, but also additional auditory ones if they are
present. For example, because of the longer nerve-conduction
times, sensory consequences of foot movements should be
centrally available only later than sensory consequences of
hand movements; thus negative asynchrony is larger in the
former case than in the latter. When auditory feedback is
added to the taps, negative asynchrony can be manipulated by
varying the delay of the auditory feedback relative to the taps
(Aschersleben & Prinz, 1997): Negative asynchrony declines
when feedback tones are added without delay and increases