<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">Ben,<DIV><BR class="khtml-block-placeholder"></DIV><DIV>I assume you were entertaining some interesting scenarios when you raise these questions. A lot of processes can happen when one maintains the eye fixation at an object or a few objects for a while. For example, during the fixation, presumably, 1) one can get shocked and one's mind goes blank (eg, seeing a dead man walking); 2) one can engage in one single retrieval for a long time until tired (eg, trying to recollect who that familiar face belongs to); or 3) one can engage in a chain of retrievals (eg, that face looks similar to Johnson's, Johnson cried yesterday because his dog died, oh, what a dog...). That's one reason why ACT-R has a modular design, so different modules can do different things in parallel (with constraints, of course). </DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>I believe trying to figure out what happens during your expert's 1500ms fixation is one reason why we do modeling. We can speculate what's going on based on his next eye-fixation, his verbal protocol, his decision and action, etc. When we have a better understanding of the process, we can simulate, predict and test its implications on baseline activation learning. Sometimes even if one is staring at a target (via the visuospatial module), but his mind may be attending to or working on something else (via other modules). In this case, I doubt the time length of fixation would strengthen the activation level of the target.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Hongbin</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><DIV><DIV>On Feb 15, 2006, at 9:30 PM, <<A href="mailto:ben.willems@faa.gov">ben.willems@faa.gov</A>> <<A href="mailto:ben.willems@faa.gov">ben.willems@faa.gov</A>> wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"><BR><FONT size="2" face="sans-serif">Please excuse my ignorance, but I am working on the other side of the cognitive modelers. That is, I run simulations using human experts in Air Traffic Control and create records of human activity quite similar to what you call a simulation trace. Ignoring for a moment that the visual system may be able to process several things within the foveal area simultaneously, how would you interpret a single 1500msec fixation on an object in terms of number of retrievals? Does that include a single retrieval or does it involve cyclic retrievals with a time constant of 50msec for the retrieval and another 50msec to push the chunk to the goal stack? Or do you assume that initially there is a retrieval followed by maintaining activation at a faster cycle time? Do you assume that activation strengthening occurs independent of the perceptual or motor event that triggers activation of the chunk? E.g., seeing an aircraft representation vs. listening to a reference to an aircraft or typing in an identifier for that aircraft.</FONT> <BR> <BR><FONT size="2" face="sans-serif">Ben Willems<BR> Engineering Research Psychologist<BR> William J. Hughes Technical Center<BR> NAS Human Factors Group (ACB-220)<BR> Building 28<BR> Atlantic City International Airport, NJ 08405<BR> USA<BR> Phone: 609-485-4191<BR> Fax: 609-485-6218<BR> E-mail: <A href="mailto:Ben.Willems@faa.gov">Ben.Willems@faa.gov</A></FONT><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">_______________________________________________</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">ACT-R-users mailing list</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="mailto:ACT-R-users@act-r.psy.cmu.edu">ACT-R-users@act-r.psy.cmu.edu</A></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="http://act-r.psy.cmu.edu/mailman/listinfo/act-r-users">http://act-r.psy.cmu.edu/mailman/listinfo/act-r-users</A></DIV> </BLOCKQUOTE></DIV><BR></DIV><BR><BR><DIV> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">-------------------------</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Hongbin Wang, PhD</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Assistant Professor</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">School of Health Information Sciences</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">University of Texas Health Science Center at Houston</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">7000 Fannin, Suite 600, Houston, TX 77030, USA</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica"><A href="mailto:Hongbin.Wang@uth.tmc.edu">Hongbin.Wang@uth.tmc.edu</A>, Tel: 713-500-3911, Fax: 713-500-3929</FONT></P> </DIV><BR></BODY></HTML>