NEST

Place:             Lecture Room, Sterling Memorial Library,
                      Yale University
                      120 High Street (entrance on Wall Street), New Haven, CT

Steven Seow and Russell M. Church (Brown University)
E-mail: Russell_Church@brown.edu

In a standard continuation timing task, participants are instructed to tap a key in synchrony with an isochronous auditory stimulus sequence (synchronization phase), and then to continue tapping at the same rate after the sequence is halted (continuation phase). During the continuation phase, a frequent finding is that the (onset-to-onset) interresponse intervals (IRIs) tend to drift, but these drifts are more likely to be statistically eliminated than explained by researchers. The present experiments focused on systematic drifts and their relationship to the (onset-to-onset) interstimulus interval (ISI), which varied from 200 to 800 ms, under several experimental conditions. The conditions included a standard continuation task (Standard), a task in which the participants did not tap during the synchronization phase (Listen), and a condition in which there was an 8-s delay between the synchronization and continuation phase (Delay). Under all conditions, there was a linear relationship between the residual IRI (IRI-ISI) and the ordinal position of the taps during the continuation phase. Under the Standard and Listen conditions the intercepts and the slopes were negatively related to the ISI; under the Delay condition the intercepts were negatively related to the ISI, but the slopes were negligible. These systematic drifts, and the differential effect of an 8-s delay between the synchronization and continuation phases, provide the basis for new interpretations of the processes involved in continuation tapping.

9:30 - 10:00
TIMING DRIFT: A 3-WAY EXTENSION OF THE WING-KRISTOFFERSON MODEL

Geoffrey Collier (South Carolina State University) and R. Todd Ogden (Columbia University and New York State Psychiatric Institute)
E-mail: Rhythmpsyc@aol.com

The Wing-Kristofferson model decomposes variance in simple isochronous rhythmic tapping into two components, one due to motor noise and the other attributed to a central clock. Our model further decomposes the clock component into two sources, one due to rate drift, and the other constituting a drift-free clock. This method has been derived analytically and studied through simulations. Application of this 3-way decomposition to a large empirical data set will be presented, where the proportion of the total variance due to the three components as a function of tempo has been analyzed. The role of certain endogenous variables, such as individual differences and the differences among the limbs, will also be discussed.

10:00 - 10:30
EFFECTS OF AGE AND TEMPO IN THE TIMING CONTROL OF RHYTHMIC PERFORMANCE: A LIFESPAN STUDY

Devin McAuley1, Mari Riess Jones2, Shayla Holub1, Nathaniel Miller1, and Heather Moynihan2 (1Bowling Green State University; 2Ohio State University)
E-mail: mcauley@bgnet.bgsu.edu

The aim of the present study was to examine the effects of age and tempo on the timing control of rhythmic performance. Two hundred eighty-nine individuals from Northwest and Central Ohio between the ages of 4 and 95 completed a battery of paced and unpaced rhythmic tapping tasks. Unpaced tapping tasks included production of spontaneous, slowest, and fastest motor tempi. Paced tapping tasks included synchronization with simple isochronous sequences and were followed by continuation of tapping at the same tempo as accurately as possible once the sequence stopped. Stimulus sequences were comprised of brief tones and presented at a range of tempi (150-1709 ms interonset intervals). The results reveal a shift in spontaneous motor tempo (SMT) between the ages of 7 and 8: The average SMT between the ages of 4 and 7 was approximately 300 ms between taps, doubling to approximately 600 ms between taps by the age of 8, with an increase in variability. Adults showed a similar, but less consistent, trend towards slower SMT later in life. Age influenced the range of possible tapping rates, as measured by the difference between slowest and fastest motor tempo measures. Children showed a large increase in tapping range with age, with younger children much more restricted in the tempo range of their tapping than older children. Adults showed the reverse age-related trend, with younger adults able to tap significantly slower and faster than older adults. Overall, unpaced tapping measures revealed a pattern of findings consistent with the paced-tapping measures. Children demonstrated large age-related improvements in synchronization performance, but the improvements were most pronounced at the slower tapping rates. Older adults showed overall worse synchronization performance compared with younger adults, but these decrements in performance were of a much smaller magnitude than the improvements observed with the children.

Laura Redi (Harvard University and Massachusetts Institute of Technology)
E-mail: redi@mit.edu

The relation between perception of rhythmic regularity in sequences of speech syllables and the timing characteristics of speech is a longstanding puzzle, since it is now well-established that acoustic isochrony among syllables is quite rare. This study investigated the relation between the perception of rhythmic regularity or perceptual isochrony and acoustic timing in a speech corpus of short read sentences produced by ten talkers. A group of listeners was trained in using a labeling system for the annotation of perceptual isochrony in speech, and they applied this system to the read speech corpus. Comparison of labels produced by the listeners made it possible to identify regions of interest (ROIs) in the speech which were heard as isochronous or anisochronous by some criterion number of listeners (e.g., the majority). Results suggest that ROIs heard as perceptually isochronous are short on the average, typically consisting of three to four beats; the longest perceptually isochronous ROI in the corpus consisted of eight beats. Inter-beat interval (IBI) durations were determined for each ROI, where IBI duration was defined as the time between the onsets of vowels in successive syllables that were heard as beats. It was found that 95% of IBIs were between 200 and 1000 ms long, for ROIs identified as perceptually isochronous by at least two listeners. These results suggest that (a) perceptual isochrony in speech persists over relatively short syllable sequences, rather than entire utterances, and (b) IBI durations in speech fall within a range which is similar to that expected for inter-beat-intervals in musical rhythms (Drake, Jones, & Baruch, 2000).

11:30 - 12:00
TIMING IN THE LONG RUN: FURTHER EVIDENCE FOR THE INDEPENDENT NATURE OF TIMING PROCESSES

Howard Zelaznik, Rebecca Spencer, and Breanna Studenka (Purdue University)
E-mail: hnzelaz@purdue.edu

We report two experiments in which we examined the timing precision of tapping and circle drawing movements. In these experiments, we had people time a 500-ms cycle, but now for longer sequences than in previous experiments. In the first experiment, subjects performed in a continuation paradigm for 95 cycles following disengagement of the metronome. We found that even for this longer trial sequence there was no evidence for a common timing process governing tapping and circle drawing. In the second experiment, we compared these long trial runs under two synchronization conditions: a constant metronome period of 500 ms, or a randomly varying metronome period between 480 and 520 ms. (Subjects were not aware of the metronome variation.) We found that the structure of timing in the tapping and circle drawing tasks was still different in each synchronization task. Overall, these two experiments provide further support for our hypothesis that timing of tapping and timing of drawing are controlled by different processes.

12:00 - 12:30
BRAIN ACTIVITY IN INTERCEPTIVE AND INTERVAL TIMING TASKS: AN fMRI STUDY

Kazutoshi Kudo (University of Tokyo and University of Connecticut)
E-mail: Kazuookudo@aol.com

There have been two major types of task in timing studies: interceptive and interval timing tasks. Using fMRI, we investigated human brain activity in performing an interceptive timing task and compared it with the activity observed during interval or reaction time tasks. In Experiment 1, we investigated the difference in brain activity between interceptive and interval timing tasks. Subjects were asked to tap their thumb with the index finger to indicate the arrival time of a moving stimulus at a target location in the interceptive task, and to anticipate the time of occurrence of consecutive stimuli in the interval timing task. In Experiment 2, we compared the brain activity in the interceptive timing task to that in a reaction time task using identical visual stimuli. Brain activity analyzed by SPM (statistical parametric mapping) suggested that brain regions corresponding to different "functional modules" participated in these tasks: time keeping (basal ganglia) in the interval timing task, and visual processing (occipital area), attention (inferior temporal lobe), and working memory (dorsolateral prefrontal cortex) in the interceptive timing task. In addition, the MT+/V5 (motion-responsive) area was activated in the interceptive timing task relative to the reaction time task. These results suggest that, depending on the information that specifies the temporal evolution of events, different brain structures can be more or less involved in anticipation of targeted events.

Scott W. Brown and Stephanie M. Merchant (University of Southern Maine)
E-mail: swbrown@usm.maine.edu

Much of the research on time and attention employs dual-task methodology to uncover patterns of interference between concurrent temporal and nontemporal tasks. Many experiments have shown that nontemporal tasks disrupt time judgments, but relatively few studies have investigated whether timing interferes with nontemporal task performance. This is an important issue, however, because a pattern of mutual interference between concurrent tasks implies that they rely on the same cognitive processes or mechanisms. The present research concerns the relation between time perception and sequence perception. We postulate that timing and sequencing draw from the same pool of attentional resources, and predict that concurrent timing and sequencing tasks should produce a pattern of mutual interference because of capacity limitations. Subjects performed timing and sequencing tasks both singly and concurrently in a series of 2-min trials. The timing task required subjects to generate a series of 5-sec temporal productions via button presses. The sequencing task involved monitoring a familiar event sequence presented on a screen and detecting omissions in that sequence. Subjects were to press a button whenever an omission occurred. An easy version of the task involved an alphabetic sequence of letters (A, B, C, ...); a difficult version involved an alphanumeric sequence of letter-number pairs (A-5, B-6, C-7,...), in which omissions could occur in either the letter or number series. Comparisons of single-task and dual-task conditions showed clear evidence of mutual interference: (a) The sequencing tasks interfered with timing by making temporal productions longer and more variable, and (b) the timing task interfered with sequencing by lengthening response times to sequence omissions and reducing perceptual sensitivity at detecting omissions. The results indicate that time perception and sequence perception are closely related, and suggest that both processes depend on a common set of attentional resources.

Jacqueline C. Shin (University of Virginia) and Richard B. Ivry (University of California, Berkeley)
E-mail: js4fh@cms.mail.virginia.edu

Fluent performance in many complex tasks requires performing a sequence of movements according to a temporal pattern. We investigated the role of the basal ganglia and the cerebellum in the integration of timing and action. Specifically, we compared performance between ParkinsonÕs patients, patients with cerebellar lesions, and healthy control participants on a serial reaction time task in which sequences were presented simultaneously in a spatial and a temporal dimension. In this task, key-pressing responses were based on spatial information, and the timing was incidental to which key was pressed. The spatial sequence was defined in terms of the location of a visual stimulus, and the temporal sequence was defined in terms of the response-to-stimulus interval (RSIs). Importantly, the two sequences were correlatedÑthey were of the same length and were presented in a fixed phase relationship to each other. Spatial sequence learning was measured by comparing performance between blocks where the stimulus location was sequenced and blocks where the stimulus location was randomized. Similarly, temporal sequence learning was measured by comparing performance between sequenced and random RSI blocks. Finally, sequence integration was measured by inserting blocks in which the spatial and temporal sequences were phase-shifted. The main results were that the healthy participants learned the individual sequences and integrated them into a common sequence representation. However, the ParkinsonÕs patients only showed individual sequence learning but not sequence integration. In contrast to both groups, the cerebellar patients did not show evidence of any sequence learning. Together, these results are congruent with the notion that the basal ganglia are involved in integrating action and timing information, whereas the cerebellum is involved in a more general learning mechanism.

2:30 - 3:00
SWITCHING MOTOR TASKS: REACHING AROUND OBSTACLES Steven A. Jax and David A. Rosenbaum (Pennsylvania State University)
E-mail: saj151@psu.edu

Researchers in the area of cognitive control frequently use the task switching paradigm to study how humans deal with an ever changing environment. A consistent finding using this paradigm with mental tasks is that reaction time (RT) increases after a required task switch (termed a Òswitch costÓ). The current research extends this paradigm to a motor task: reaching around obstacles. We had participants perform reaching movements between targets in the presence of or in the absence of an intervening obstacle. Repetitions and switches of obstacle-present and obstacle-absent trials occurred randomly but with equal frequency within a block. Results showed a number of similarities and differences between motor and mental task switching. Like mental task switching, the switch cost for motor tasks was not reduced with practice and was greater for the easier task (obstacle-absent trials) than for the more difficult tasks (obstacle-present trials). Unlike mental task switching, the switch cost was observed in the kinematic properties of the movement (movement time and hand-path curvature) but not in RT. Also unlike mental task switching, the switch cost was not limited to the trial after the switch. Future research will examine the similarities and differences between motor and mental task switching.

3:30 - 4:00
COGNITIVE ACTIVITY, DIRECTED ATTENTION, AND HANDEDNESS IN BIMANUAL COORDINATION DYNAMICS

Geraldine L. Pellecchia (University of Hartford and University of Connecticut)
E-mail: pellecchi@hartford.edu

The present research combines the study of directed attention and handedness by Amazeen et al. (JEP:HPP, 1997) and the study of cognition and coordination by Pellecchia and Turvey (JMB, 2001). Handedness, direction of attention (to the left, frontward, or right), and cognitive activity were manipulated in a 1:1 frequency-locking task. Fifteen right-handed and fifteen left-handed participants performed in-phase oscillations of two hand-held pendulums. Participants held the pendulums so that 40 cm of the 1 m length extended vertically above the hands. Direction of attention was manipulated by having participants tap the oscillating pendulum on targets hung over the right or left hand. Participants performed the coordination task singly and concurrently with the cognitive task of counting backward by 3s. In concert with the findings of Amazeen et al., asymmetries in the coordination dynamics arose both from handedness and directed attention. Right-handed participants tended to be more right-leading than left-handed participants. Directing attention to the right resulted in a coordination dynamic that was more right-leading, whereas directing attention to the left resulted in a coordination dynamic that was more left-leading. Stability was lowest for attending left, intermediate for attending right, and greatest for attending frontward. Performing a concurrent cognitive task amplified the asymmetry of inter-limb coordination due to directed attention when participants attended to the left pendulum. That observed shift in attractor location away from the required in-phase relation was not dependent upon handedness. Neither direction of attention nor handedness impacted performance on the cognitive task. It appears that the coupling of cognitive and coordination tasks amplified the asymmetrical dynamics of the least stable coordination pattern.

Hyeongsaeng Park (University of Connecticut and Haskins Laboratories)
E-mail: Hyeongsaeng.Park@huskymail.uconn.edu

The Haken-Kelso-Bunz (HKB) equation expressing the dynamics of interlimb rhythmic coordination possesses reflectional symmetry. Past research suggests that when elements are introduced to break the symmetry, the dynamicsÕ fixed points or attractors abide by a variant of the Extended Curie Principle. That is, the induced symmetry breaking produces solutions (fixed points) of the HKB dynamics that are related by reflectional symmetry. The present research was motivated by the question of whether the hypothesis of symmetry redistribution could accommodate recent findings of spatially asymmetric HKB dynamics that suggested an origin in the contrasting stabilities of local muscular organizations. In two experiments, left and right forearms generated oscillations in a frontoparallel plane about the same (Experiment 1) or different (Experiments 1-2) axes of rotation that created spatial asymmetry. The oscillations were of two pendulum-like manipulanda with eigenfrequencies that were either the same or different. The results of Experiment 1 were favorable to the Extended Curie Principle for both fixed point and fixed-point stability measures and to the ancillary hypothesis of a dissociation of attractor location and attractor strength. In Experiment 2 manipulations of movement speed revealed that the pattern of symmetry redistribution, for both fixed point and fixed-point stability measures, was consistent over speed variations. They also revealed that movement speed interacted with strict spatial asymmetry in the same way that movement speed interacts with strict temporal asymmetry. Discussion will focus on the implications of the data for the muscle-stability and symmetry-redistribution hypotheses with respect to the consequences for coordination dynamics of induced symmetry breaking. It also will raise the challenging question of a generalized imperfection parameter for the HKB equation.