From Greg Williams (930120)
I think the burgeoning DB + critique thereof could be put to good (if
mischievous?) use. Why not work up the quotes and challenges/reinterpretations
and send copies to lots (ca. 50?) of "biggies" in the "harder" (???) end of
establishment psychology? An epistle from CSGnet to YOU: we have some problems
with the basic assumptions... might you be able to set us straight. Even if
not one joins the net, I bet at least a few will have their eyes opened a bit
to the fact that they have been glossing over some difficulties. Anybody else
up for this? The dialogue needs to escape the confines of the net, in my
opinion -- without the necessity of submitting to a journal. I think we need
ongoing interactions with REAL "devils."
OK, Rick, here's some more. (You ARE a nice guy, despite what they say about
you on the net.)
253 - "... Keele and Posner ([J. EXP. PSYCHOL. 77, 155-158] 1968).... trained
their subjects to move a hand held stylus (like a pencil) to a small target a
few centimeters away. Knowledge of results about MT [movement times] was
provided, and subjects were trained to move in either 150, 250, 350, or 450
msec, in separate sessions. Then, when the subjects had perfected the MTs, on
certain trials (unpredictable to the subjects) the experimenters would turn
off the room lights when the subjects left the starting position, so that the
remainder of the movement would have to be made in the dark. The logic was
this. If, in the 250-msec condition, for example, the lights-on condition
produced less movement error than the lights-off condition, then the lights
being on must have contributed to accuracy, and the implication would be that
vision was being used for movement control. Conversely, if no differences in
accuracy were obtained between the lights-on and lights-off conditions, then
the implication would be that vision was not being used in the response and
that visual feedback processing time was greater than the corresponding MT in
these responses.
Keele and Posner (1968) measured the probability of missing the target for
the four MT categories for the lights-on and the lights-off conditions... The
most important finding is that, in the 150 msec MT condition (the actual MT
was 190 msec), about as many target misses were recorded when the lights were
on (68 per cent) as when the lights were off (69 per cent). The authors argued
that when the MT was 190 msec or less, the vision of the hand or target did
not contribute to movement control; thus, they argued that using visual
feedback required at least 190 msec (one RT [reaction-time]) to process. Also,
as the MTs increased, an advantage began to develop for having the room lights
on. When the MT was 260 msec, there were 47 per cent misses for the lights-on
condition and 58 per cent misses for the lights-off condition. The lights-on
advantage increased steadily as the MT increased, so that with a 450 msec MT,
the lights-off condition had 47 per cent misses and the lights-on condition
had only 15 per cent....
254 - Hawkins et al. [ms. in prep.] performed a series of experiments much
like that of Keele and Posner, except that their subjects practiced for a
block of trials with vision always presented, and then a block of trials with
vision always withheld, thus eliminating the problem of having the vision
unexpectedly removed. They plotted the total variability around the target...
as a function of the MT... The lights-on condition was beneficial at all MTs,
even for those as short as 100 msec! These data suggest that vision, when its
presence can be expected, can be used in far less time than the 190 msec that
Keene and Posner suggested, perhaps with visual processing times as short as
100 msec.... Another experiment showed that the advantage of the lights-on
condition vanished when the MTs were 80 msec..."
255 - "Taken together, these findings seem to provide a contradiction to the
general notion that vision presented in the environment cannot influence a
movement until all of the stages of information processing have been completed
-- that is, until about 190 msec have elapsed. How can the advantage of vision
occur when the MT is far shorter than this 190 msec? One answer is that vision
in these situations is not processed like a suddenly presented stimulus to
which a response must be made, because more or less continuous vision of the
hand and target occurs during the movement....
Another possibility is that vision 'tunes' the motor system for accuracy...
It is possible that corrections in the movement do not occur at all, but that
vision prepares the spinal apparatus for the ongoing movement... These ideas
are speculative..."
299 - "... it does not make sense to claim that motor programs operate without
feedback."
As ever,
Greg