Brain, Behavior, and the Emergence of Cognitive Competence

A program-project grant supported by the National Institute of Child Health and Human Development (HD-38051)

Research Updates:

RESEARCH UPDATE - AUGUST 2003

ADMINISTRATIVE CORE

PRIMATE SPATIAL COGNITION AND MEMORY

THE EMERGENCE OF COGNITIVE CONTROL

THE EMERGENCE OF UNCERTAINTY MONITORING

NEUROANATOMICAL AND NEUROFUNCTIONAL CORRELATES OF COGNITIVE COMPETENCE

ADMINISTRATIVE CORE

Rumbaugh festschrift. A major activity of Year 4 was the scheduling and hosting of a celebration of Dr. Rumbaugh's ongoing career. The main session of "Emergents and Rational Behaviorism: A Festschrift in Honor of Duane Rumbaugh" was hosted at Georgia State University in October, with a secondary festschrift symposium held in coordination with the annual meeting of the Southern Society for Philosophy and Psychology. A total of 36 presentations, including graduate student posters, were made in the festschrift sessions. The speakers included investigators from the present program-project and other distinguished scholars representing comparative psychology, primatology, and anthropology.

Festschrift book. We are currently heavily engaged with editing the book that will result from this festschrift. The collection of essays in honor of Duane Rumbaugh is scheduled to be delivered to the publisher on 15-August-03.

Hard Data Café colloquia. The project continued its schedule of meetings to discuss the latest scientific findings in conjunction with the Hard Data Café colloquim series at Georgia State University. Dr. Smith and Dr. Washburn made presentations , and Dr. Beran coordinated the visit of a guest lecturer from Japan (Dr. Dora Biro).

Common Territories Symposium. As was discussed in the Year-4 report, a special issue of the International Journal of Comparative Psychology was guest edited this year by Dr. Washburn, with a contribution by Dr. Smith.

Intelligence of Apes and Other Rational Beings. A major effort supported by the administrative core was the revision, indexing, and completion of this book, co-authored by Dr. Rumbaugh and Dr. Washburn and published by Yale University Press. The book will hit the shelves in June, 2003. It promises to be a significant contribution to the literature on intelligence and learning, an entertaining review of decades of research with apes and monkeys, and a fitting testament to the sustaining investments of the NICHD.

http://www.gsu.edu/~lrc. Major revisions were made to the Language Research Center website An updated list of project-supported publications and presentations appears at this URL. This web page has proven to be vital for recruiting top-notch students to our research, such as the two new students who will be joining the team in Year 5.

PRIMATE SPATIAL COGNITION AND MEMORY

Mazes. We previously showed that monkeys and apes show nascent planning abilities while solving two-dimensional alley mazes using a joystick. The aim of the experiment conducted by Fragaszy this past year was to assess the contribution of scaffolded experience to the development of spatial planning in monkeys and apes. To accomplish this, we compared the performance of monkeys and chimpanzees encountering alley mazes in a random order to those encountering the mazes in a scaled order, from easy to difficult. Four monkeys have completed the series of 192 novel mazes presented in a random order. This study will constitute the Master's thesis for Erica Hoy at the University of Georgia. Data are currently being collected with three chimpanzees at Yerkes National Primate Research Center with the assistance of W. Hopkins and A. Murnane. Capuchins encountering the mazes in random order have far more difficulty solving them initially than those that encounter them in an ordered series.

Primate geometry. Our general question is: What constitutes a "shortest path" for a nonhuman primate? We continue to address this question in chimpanzees and rhesus macaques in computer-presented tasks, including maze-, multi-target-, and open-field tasks. Our aim in the open-field tasks is to assess each subject's assumptions about which route is the shortest when the space in question does not contain barriers. The shortest distance between two points in a digital space is not always a straight line. We presented nonhuman primate subjects with open-field tasks in a digital format and are analyzing the extent to which the subjects adhere to straight-line movement to targets. In the open field tasks, and also in the other tasks that include barriers, we compare each subject's path to the optimal, least-distance routing. In Year 4, we collected data on five macaques and four chimpanzees in computer-presented open field and multi-target tasks, as described in the grant proposal. In Year 4, we also obtained data on four chimpanzees at the Yerkes National Primate Research Center, on a systematic barrier-and-detour task, with assistance from W. Hopkins. The task is much simpler than a maze, but it provides an exceptionally sensitive measure of individual and group differences in the efficiency and organization of movement. We have prepared one manuscript for publication on this barrier-and-detour task (Menzel & Menzel, in prep).

Disappearing barrier tasks. Our previous data on chimpanzees and macaques suggest that there is a large difference between humans and nonhumans in how well a participant can circumvent barriers that are shown to the participant prior to the initiation of movement but then rendered invisible. To determine the asymptotic performance of test-wise chimpanzees on a disappearing barrier task, Menzel presented the four LRC chimpanzees with 20 replications of a delayed-response version of the systematic barrier-and-detour task mentioned earlier. Each replication of the task entailed solving a set of 128 problems (2,560 trials per animal in total). The data are currently being analyzed.

Development of improved pointing devices. In Year 4, Menzel collected additional data on a male chimpanzee's use of a joystick-controlled laser pointer to pinpoint the locations of hidden objects in an outdoor wooded area. In brief, the chimpanzee watched while an experimenter hid an object in the woods outside his outdoor enclosure. After a delay, a caretaker who did not know where the object was hidden gave the chimpanzee access outdoors to a joystick. The joystick controlled the orientation of a 5-milliwatt laser pointer. The laser pointer was located outside the chimpanzee's outdoor enclosure, so that the chimpanzee could not touch the laser pointer itself. To obtain the object, he had to manipulate the joystick manually such that the laser dot came to rest on the correct location. In trials with distances up to 15 m, the chimpanzee indicated the location of the hidden object in a large outdoor area with high precision.

Memory in outdoor tasks. In Year 4, Menzel completed an experiment that demonstrates that a female symbol-competent chimpanzee could a) retain and report the locations and types of 6 different items in 6 different locations in a large outdoor test area and b) retain and convey the approximate number of items of hidden in a single given location in the woods, over a range of 1-12 items. Specifically, the number of times that the chimpanzee recruited a person to the location was highly correlated (r=0.86) with the number of items the chimpanzee had seen hidden in the location. C.

Significance. The findings help to characterize spatial cognition and memory capabilities in primates.

Plans. Menzel's Year 5 activity will include collection of data on chimpanzees, rhesus, and capuchin monkeys in computer-presented foraging, traveling salesman, and barrier tasks, as described in the grant proposal, and preparation of manuscripts based on these data. Year 5 aims for Menzel's portion of the maze study are to collect data on additional rhesus monkeys. Testing in the outdoor enclosures will continue as described in the grant proposal. Fragaszy's Year 5 activity will include a) completion of testing with chimpanzees with the mazes in random order and preparation of manuscripts from the set of studies on mazes; b) assessment of asymptotic performance on two-dimensional alley mazes by capuchins, through presentation of the original series of 192 mazes in ordered fashion in replications, c) assessment of the equivalence for capuchin monkeys and chimpanzees of two-dimensional and three-dimensional images in spatial search tasks, using touch-screen methodology and an innovative "virtual search" task (a portion of K. Leighty's doctoral dissertation at the University of Georgia), and d) piloting of tasks concerning analogical reasoning in monkeys solving spatial problems. This work will contribute to the dissertation research of Erica Hoy.

Publications.

Fragaszy, D., Johnson-Pynn, J., Hirsh, E., and Brakke, K. (2003). Strategic navigation of two-dimensional alley mazes: Comparing capuchin monkeys and chimpanzees. Animal Cognition, 6, 149-160.

Leighty, K., and Fragaszy, D. (2003). Primates in cyberspace: Using interactive computer-formatted tasks to study perception, and action in nonhuman animals. Animal Cognition, 6, 137-139.

Fragaszy, D., Visalberghi, E., and Fedigan, L. (in press). The complete capuchin. The biology of the genus Cebus. Cambridge: Cambridge University Press. Menzel, C.R. (submitted). Progress in the study of chimpanzee recall memory. In: H. Terrace & J. Metcalfe (Eds.) The Missing Link in Cognition: Origins of Self-reflective Consciousness. Oxford University Press.

Menzel, C.R., Savage-Rumbaugh, E.S. & Menzel, E.W., jr. (2002). Bonobo (Pan paniscus) spatial memory and communication in a 20-hectare forest. International Journal of Primatology, 23, 601-619.

Menzel, C.R. & Kelley, J.W. (2002). Spatial cognition and memory in a symbol-using chimpanzee. American Journal of Physical Anthropology, Supplement 34, 112. ABSTRACT.

Menzel, C.R., Kelley, J.W. & Sanchez, I.C. (2002). A chimpanzee's comprehension of televised spatial information. American Journal of Primatology, 57, 79. ABSTRACT

Menzel, E.W., Jr. & Menzel, C.R. (submitted). "Simple" detour problems reconsidered. In D. Washburn (Ed.) Festschrift volume in honor of Duane Rumbaugh.

THE EMERGENCE OF COGNITIVE CONTROL

Study 1.1 C General Tests of Attention. An abbreviated version of the ASAP attention battery was administered to 85 children at the Howard School. The children, who ranged in age from 6- to 17-years, also completed the ANT described below. Many of these children came to the Howard School from traditional educational settings, where they had been diagnosed with attention deficits, reading disabilities, and other learning problems. A report of these findings were presented at the meeting of the American Psychological Society and at the meeting of the International Conference on Children and Adults with Attention Deficit and Hyperactivity Disorder.

Study 1.2. The costs and benefits of cuing. This year saw a significant improvement in this project relative to the proposal. Michael Posner and colleagues developed a new variation on the cuing paradigm called the Attention Network Test (ANT). The ANT is unique in that it provides separate measures of three different networks of attention. A monkey-friendly version of the ANT was programmed and administered. This study is ongoing.

Study 1.1 D Attention Profiles & Uncertainty Monitoring. Undergraduate volunteers (N = 273) were tested on the ASAP attention battery, an uncertainty monitoring task, and numerous other search tasks. Preliminary results from this study were presented at the meeting of the Southern Society for Philosophy and Psychology and at the meeting of the American Psychological Society.

Study 1.4 and Study 1.7 Visual search and Vigilance. The search data collected last year were submitted for publication. Additional search data were collected from human participants as described above to be compared with vigilance decrements across a 20-minute watchperiod.

Study 1.6 Selective tracking. A report of selective tracking performance by human participants was presented at the Southern Society for Philosophy and Psychology.

Study 2.2 Stroop for chimpanzees. A chimpanzee, Lana, was presented with a task designed to determine if she would exhibit a Stroop effect in accuracy or response latency. Lana was presented with either a colored patch (colored blue or yellow), a lexigram representing the term "name-of" in the color yellow or the color blue, a lexigram representing a color in the congruous color (lexigram yellow in color yellow or lexigram blue in color blue), or a lexigram representing a color in the congruous color (lexigram yellow in color blue or lexigram blue in color yellow). Although Lana showed some signs of a Stroop effect, this effect was not consistent or strong.

Study 3.1 and 3.4 Meaningful failures and The "apparatus artifact". Performance on the computerized tasks were compared with performance with a manual test apparatus. Monkeys were tested in a two-choice discrimination learning paradigm with left-right mirror-image stimuli. The monkeys were unable to learn the task with either apparatus, in contrast to the "apparatus artifact" hypothesis. These findings were presented at the Rumbaugh festschrift.

Study 3.3 B Practicing executive control. We systematically manipulated the environmental constraints, the executive constraints, and the executive constraints on attention. Manipulations of environmental cues (e.g., movement, flashing) versus executive cues (incentive) showed that whereas the former influenced attention for monkeys and human adults, the adults were uniquely responsive to the executive constraints. Similar results were obtained when environmental cues were contrasted against experiential (priming) and executive constraints (instruction).

Study 4.A. Relating cognitive control to other aspects of cognitive competence. Two new studies were conducted on numerical competence by rhesus monkeys. One task was modeled after the maze-running paradigm made popular by Burns and Capaldi. Monkeys understood Arabic numerals to signal the number of reinforced trials that would precede each nonreinforced trial. In the second study, monkeys responded at levels significantly better than chance to multiple numerals positioned with a simple maze. Two studies also were conducted with chimpanzees. In the first of two studies designed to examine numerical cognition and memory, two chimpanzees made numerousness judgments of nonvisible sets of items. In Experiment 1, 1 to 10 items were dropped, one-at-a-time, into one opaque cup, and then an additional 1 to 10 items were dropped, one-at-a-time, into another opaque cup. In Experiment 2, a third visible set was made available after the sequential presentation of the first two sets. In Experiment 3, one of the two initially presented sets was reduced in number by the sequential removal of 1, 2, or 3 items. Both chimpanzees performed above chance levels for the removal of one item but not for the removal of more than one item. A manuscript containing these data has been submitted for publication to Journal of Comparative Psychology. In a second study, four chimpanzees were highly accurate in selecting the larger of two concurrent accumulations of bananas in two opaque containers over a span of 20 minutes. Bananas were placed, one at a time, into one of the two opaque containers outside of the chimpanzees' cages. The chimpanzees provided the first demonstration by nonhuman animals of extended memory for accumulated quantity. These data are to be published in Psychological Science.

Study 4.B. Biobehavioral studies of cognitive control. We began a study on the effect of gingkgo biloba on attention and memory performance. We also completed a study on the effects of transcranial magnetic stimulation on perception and uncertainty monitoring. Finally, we looked at the functional cerebral asymmetries that characterize human numerical cognition. Undergraduates were tested on perceptual and judgment tasks in a divided visual hemifield task. These latter data were presented at a meeting of the Southern Society for Philosophy and Psychology.

Significance. Increasingly, these studies are revealing the nature of attention across species, the factors that control attention for human adults, children, and nonhuman primates, the biological basis of attention, and the training methods that may improve attention skills.

Plans. One major goal of Year 5 is to convert the substantial corpus of data that have been collected, as evidenced by the number of professional presentations, into publications. We will complete the ongoing Stroop, ANT, and vigilance studies. We anticipate completion of a "factors of attention" study with at least one monkey in Year

Publications.

Bovet, D., & Washburn, D. A. (in press). Rhesus monkeys (Macaca mulatta) categorize according to social dominance. Journal of Comparative Psychology.

Washburn, D. A. (in press). The games psychologists play (and the data they provide). Behavior Research Methods, Instruments and Computers.

Washburn, D. A., Gulledge, J. P, & Rumbaugh. (Submitted). Does language link memory for what and where? Submitted to Science.

Washburn, D. A. (submitted). The control of attention in visual search. Submitted to Spatial Cognition.

Beran, M. J., & Beran, M. M. (in press). Chimpanzees remember the results of one-by-one addition of food items to sets. Psychological Science.

Rumbaugh, D. M., Beran, M. J., & Pate, J. L. (2003). Uncertainty monitoring may promote emergents. Behavioral and Brain Sciences, 26, 353.

Beran, M. J., & Washburn, D. A. (2002). Chimpanzee responding during matching to sample: Control by exclusion. Journal of the Experimental Analysis of Behavior, 78, 497-508.

THE EMERGENCE OF UNCERTAINTY MONITORING

Experiment B3. In Year 4, two monkeys completed about 100,000 training trials of a task designed to examine uncertainty responses in a situation in which reinforcement is not directly linked to trial-by-trial performance. This study, for which human-participant testing was completed in previous years, is ongoing. Experiment A1 and A4. The goals of these two experiments were combined in a single task to determine whether animals will respond appropriately (as will human participants, as reported previously) in a three-region discrimination task. In Year 4, over 103,000 trials were collected for this study. However, progress on this study was hampered substantially by the death of one of the original and most experienced test monkeys.

Experiments D1, D3, and D4. This experiment was designed to test whether the uncertain response could be used adaptively when long retention intervals, brief presentation time, or stimulus masking make responding correctly in a match-to-sample task more difficult. Two monkeys continued to train in this paradigm (see last year's Progress Report), producing about 65,000 in 600 animal-sessions during Year 4. These animals will soon be moved into more complicated phases of the task.

Experiment D3 and K2. In conjunction with Dr. Hopkins's TMS project, one rhesus monkey was tested on a divided visual field task in which brief stimulus displays were used and the uncertain response was always available. Not only did this monkey use the uncertain response (without training specific to this task-see below) generally on trials with brief stimulus presentations, but he was significantly most likely to use the escape response on trials in which stimulus processing was disrupted by transcranial magnetic stimulation. This study is ongoing.

Experiment B2. The monkeys in our colony have substantial experience with tasks that generate uncertainty, but that have never allowed the animals to express their awareness of uncertainty (if indeed they do monitor their own confidence). For example, many thousands of problems of two-choice discrimination learning have been completed, and the monkeys do not know, by design, how to respond on Trial 1 of each new problem. We tested the monkeys' use of the uncertain response on tasks with novel stimuli for which there is no reinforcement history. The four animals were significantly more likely to use the uncertain response on Trial 1 than on any subsequent trial of a problem. A similar pattern was observed when the uncertain response was made available for the first time in discrimination learning or matching-to-sample tests involving left-right mirror-image stimuli. We have a large corpus of data showing that monkeys do not distinguish between mirror-image stimuli (e.g., b and d). Interestingly, the monkeys also seem to know this, as they are significantly likely to use the uncertain response on such trials-even though they had never been specifically trained to do so.

Research with human participants. A total of 834 human participants were tested in Buffalo in 23 experiments. These studies included tests of uncertainty monitoring in a delayed matching-to-sample task (to complement Experiments D1, D2 and D4 described above); the reinforcement-free uncertainty paradigm described above (Experiment B3); an analog of Shettleworth's "uncertainty" task; and several experiments on categorization and process-dissociation.

Project development. Software was written for seven research projects (General Uncertainty-Monitoring Paradigm #1, General Uncertainty-Monitoring Paradigm #2, Nonverbal Process Dissociation Paradigm, Uncertainty Monitoring in a Dense-Sparse Discrimination (short, attentional-battery version), Uncertainty-Monitoring in a Numerical-Discrimination Task (array/quantity version), Uncertainty-Monitoring in a Numerical-Discrimination Task (symbolic version), and Uncertainty-Monitoring in a Categorization Paradigm). Pilot data were obtained from 185 human participants (see above) for the first three of these projects. Data from the fourth paradigm are described in Dr. Washburn's progress report.

Significance. 1.Monkeys appear to have at least a rudimentary capacity to make multiple retrospective confidence ratings within a density discrimination task (E1). 2. We are developing ways to dissociate reinforcement history from use of the uncertain response (A4 and B3). 3. We have developed a number of novel tasks to demonstrate functional metacognition, even without prior training.

Plans. 1. Complete ongoing studies, including the various conditions of the DMTS paradigm. 2. Test monkeys on numerical-based metacognition. 3. Test monkeys on general metacognition paradigm developed in fourth year 4. Complete monkey testing of D1, D2, and D4. 5. Write and submit reports for completed studies on uncertainty and categorization.

Publications.

Smith, J. D. (2002). Exemplar theory's predicted typicality gradient can be tested and disconfirmed. Psychological Science, 13, 437-442.

Smith, J. D., Shields, W. E., & Washburn, D. A. (2003). The comparative psychology of uncertainty monitoring and metacognition. Behavioral and Brain Sciences, 26, 317-373.

Smith, J. D., Minda, J. P., & Washburn, D. A. (2003). Category learning in rhesus monkeys: A study of the Shepard, Hovland, and Jenkins tasks. Revised and submitted for publication.

Smith, J. D. (in press). Why cognitive psychologists should know comparative psychology; why comparative psychologists should know cognitive psychology. International Journal of Comparative Psychology.

Shields, W. E., Smith, J. D., Guttmannova, K., & Washburn, D. A. (2003). Confidence judgments by humans and rhesus monkeys. Submitted to the Journal of General Psychology.

Smith, J. D. (2003). Studies of uncertainty monitoring and metacognition in animals and humans. In J. Metcalfe and H. Terrace (Eds.), The missing link in cognition: Self-knowing consciousness in man and animals. Oxford, UK: Oxford University Press.

Smith, J. D. (In prep). Species of parsimony in comparative studies of cognition. To appear in Emergents and Rational Behaviorism: A Festschrift in Honor of Duane M. Rumbaugh. Written and submitted in May, 2003.

Smith, J. D. (in prep). Conflicting mathematical transformations in the exemplar model.

NEUROANATOMICAL AND NEUROFUNCTIONAL CORRELATES OF COGNITIVE COMPETENCE

During Year 4, we have completed three major components of the proposed studies. First, more MRI scans have been collected and we have a) analyzed asymmetries in new cortical areas (e.g., central sulcus, postcentral gyrus), and b) assessed the relationship between cortical areas asymmetries and behavioral asymmetries (e.g., handedness) as well as the relationship between asymmetries in different cortical areas (e.g., planum temporale and sylvian fissure). Also, we have begun analysis of asymmetries in sub-cortical structures (e.g., cerebellum) to determine the comparative basis of asymmetries in these regions relative to cortical areas.

Second, we have conducted new studies on facilitatory and interference effects of transcranial magnetic stimulation (TMS) in monkeys. In particular, we have systematically assessed the effect of TMS in the computerized global/local task involving the visual discrimination of hierarchical compound stimuli in two monkeys. In one study, TMS delivery occurred during encoding of the stimulus. In this condition, one monkey showed no disruptive effects of TMS but consistently shorter reaction times in the TMS condition as compared to baseline and sham conditions, irrespective of side of stimulation. The second monkey also a similar facilitatory effect of TMS during stimulus encoding, but only when stimulation occurred on the hemisphere contralateral to the hand used for manipulating the joystick. In a second study, TMS delivery occurred during retention of the stimulus (the task involved a 2 sec delay between stimulus encoding and discrimination). In this condition, TMS delivery resulted in marked increases in error rates for subject one. This disruptive effect of TMS was less marked for subject two. TMS was also used in conjunction with Dr. Smith's project to determine whether monkeys would respond appropriately to stimulation-induced uncertainty. Given the option to escape any trial on which they were uncertain, monkeys were significantly most likely to use this "uncertain response" on exactly those trials in which TMS had been used to disrupt stimulus processing. This study is ongoing.

To exploit further the potential of our TMS apparatus as a fruitful research tool for studying the relation of brain and behavior in nonhuman primates, we have developed, with the consultation of Dr. Epstein, a new iron-core TMS coil that has been reduced to the minimum theoretical dimensions possible. No stimulating coils of such small dimensions are available in the market, thus potentially affording us with higher spatial resolution in targeting separate regions within one hemisphere. We have already pilot-tested our new coil with two monkeys by successfully obtaining overt motor twitches of the hand and arm muscles when stimulating over the primary motor area. Motor threshold values have also been already assessed using psychophysical techniques. We are now in the process of obtaining estimates of the distribution and size of the induced electric field for this new coil, which would allow us to know the gain in spatial resolution for stimulating separate regions within one hemisphere.

Third, we have started implementing apparatus modifications as well as training procedures to apply our TMS methodology and procedure with chimpanzees. A cage has been partially modified to allow an experimenter to safely place the TMS coil over the left or right hemisphere of a chimpanzee. A chimpanzee at LRC has being trained to work on computerized tasks inside the modified cage section, while keeping the head in position for coil placement. The chimpanzee has also been gradually shaped to accept low-intensity TMS while working on a task. Finally, we have started preliminary data collection and analyses for the facial discrimination tasks with both monkeys and chimpanzees.

Significance. The significance of these findings is two-fold. First, with respect to the MRI studies in great apes, we have found the first consistent evidence of an association between asymmetry of primary motor areas and handedness in great apes. These findings are congruent with studies on the neurobiological basis of handedness in humans, thus showing the full potential of using the great ape as an animal model to further our understanding of the origin of hemispheric specialization. Second, the TMS findings in monkeys show the first evidence of a) a facilitatory effect of TMS in a cognitive task as well as b) a disruption of short-term memory induced by TMS in a nonhuman primate. Overall, this evidence clearly shows the effectiveness of the TMS apparatus developed by us as a versatile and powerful tool for studying the relation of brain and behavior in nonhuman primates. Moreover, the new smaller coil we have recently developed will increase our ability to selectively disrupt the activity of circumscribed areas on the right and left hemispheres, thus affording us with an even more powerful way to explore the possible presence of localized and lateralized cognitive functions in monkeys and chimpanzees.

Plans. In Year 5, three major projects will be completed. First, all current analyses of the MRI studies will be completed and submitted for publication. We will also initiate and complete analysis of asymmetries in more sub-cortical structures to determine the possible relationship of asymmetries in these regions relative to cortical areas. Second, we will collect additional TMS data in the monkeys for the global/local task, and will initiate and complete collection of TMS data for the facial discrimination task. Lastly, to further elucidate neural systems involved in perception and cognition in primates we will initiate and complete collection of TMS data with chimpanzees for both the global/local and facial discrimination tasks.

Publications.

Cantalupo, C., Pilcher, D.L, & Hopkins, W. D. (in press). Are planum temporale and sylvian fissure asymmetries directly related? A MRI study in great apes. Neuropsychologia.

Cantalupo, C., & Hopkins, W. D. (in press). On assessing the asymmetry of Broca's area homologue in great apes using gross morphological landmarks: a commentary on Sherwood et al. (2003). The Anatomical Record.

Cantalupo, C., Gulledge, J., Washburn D.A., & Hopkins, W.D. (submitted). Computer-driven transcranial magnetic stimulation (TMS) with a nonhuman primate (Macaca mulatta). Behavior Research Methods, Instruments, & Computers.

Fernández-Carriba, S., Loeches, A., Morcillo, A., Washburn, D. A. & Hopkins, W.D. (in press): Human assessment of chimpanzee facial asymmetry. Laterality: Asymmetries of Body, Brain & Cognition.

Hopkins, W. D., Hook, M., Braccini, S., & Schapiro, S. J. (in press). Population-level right handedness for a coordinated bimanual task in chimpanzees (Pan troglodytes): Replication and extension in a second colony of apes. International Journal of Primatology.

Leavens, D. A., Hopkins, W. D., & Thomas, R. (in press). Referential communication by chimpanzees (Pan troglodytes). Journal of Comparative Psychology.

Leavens, D. L., Hostetter, A., Wesley, M. J., & Hopkins, W. D. (in press). Tactical use of unimodal and bimodal communication by chimpanzees (Pan troglodytes). Animal Behaviour.

Hopkins, W. D., Russeel, J. L., Hostetter, A., Pilcher, D., & Dahl, J. F. (in press). Grip morphology, dermatoglyphics, and hand use in captive chimpanzees. American Journal of Physical Anthropology.

Hopkins, W. D., & Cantalupo, C. (submitted). Speechless asymmetries: Handedness in chimpanzees correlates with primary motor but not with homologous language areas.

Cantalupo, C., Freeman, H., & Hopkins, W. D. (submitted). Cerebellar asymmetry in great apes: an MRI study.