Auditory streaming: Competition among alternative organizations

It has been suggested that the ON and OFF components of the auditory evoked potential (AEP) may be mediated by independent physiological mechanisms and that the response to a brief tone consists of overlapping ON and OFF responses. Two experiments were performed to evaluate these proposals. First, AEPs were recorded to tonebursts of various durations presented at a fixed rate. As the tonebursts were made longer, they evoked smaller ON responses and larger OFF responses, particularly when either response followed the other by less than 5 sec. This indicates that ON and OFF responses are not physiologically independent. Second, the AEP to a 25-msec tone was compared with the ON response to a 2,000-msec tone. At an interstimulus interval of 4 sec, the difference wave formed by subtracting the latter AEP from the former contained clear N₁ (ca. 100 msec) and P₂ (ca. 180 msec) components, which have been interpreted as an OFF response by some authors. These components in the difference wave were greatly reduced or even inverted at 10-sec interstimulus intervals, however, where interactions between ON and OFF responses to successive stimuli were minimized. This result indicates that any residual OFF response in the AEP to a brief tone is very small in amplitude, if present at all.     

An inexpensive pure-tone pattern generator

A low-cost sound pattern generator that is remotely programmable has been developed to produce pure-tone auditory patterns. The device, which is compatible with relay programming equipment, can generate either of two auditory patterns in the sequence ABA or BAB. The generator features an independently settable range of ON and OFF durations (0.1 to 1.0 sec) for pure-tone bursts and a selectable range (0.2 to 2.0 sec) of intercycle intervals. The inexpensive construction cost coupled with the flexibility of the timing characteristics of the generator should make it of interest to a wide variety of auditory researchers.     

Use of the gait deviation index for the evaluation of patients with Parkinson's disease

The authors aimed to determine whether the Gait Deviation Index (GDI) could be feasible to characterize gait in patients with Parkinson's disease (PD) and evaluate outcomes of levodopa treatment. Twenty-two PD participants were evaluated with clinical examination and 3-D quantitative gait analysis (GDI was calculated from gait analysis) in 2 states (OFF and ON) after taking levodopa. Twenty age-matched healthy participants (CG) were included as controls. The GDI value in the OFF state was 83.4 ± 11.5 (statistically different from CG) while clinical scales demonstrated a moderate-severe gait impairment of these patients. Significant improvements are evident from clinical scores and by GDI values in the ON state. The mean GDI for the ON state (GDI(ON): 87.9 ± 10.4) was significantly higher than in for the OFF state (GDI(OFF): 83.4 ± 11.5), indicating a global gait improvement after the treatment. The results show that GDI has lower value as an indicator of pathology in PD patients than in quantifying the effects of levodopa treatment in PD state.     

A portable solid-state stimulus programmer

This paper describes a miniature solid-state timing device particularly useful for presenting repetitive signal sequences in classical conditioning experiments. The device uses transistors, silicon-controlled rectifiers, and four-layer diodes, and is powered by 20-hour rechargeable nickel-cadmium batteries. Visual monitoring is provided for the unelapsed ITI and battery charge. Ranges are; ITI, 15 sec. to 5 min., ISI, 0–50 secs., CS duration, 0.5 to 30 sec., US duration, 0.5 to 30 sec. The CS and US durations are adjustable and the onset of the latter may be at any time after the CS onset. Cycling is continuous and automatic; the outputs are in the form of relay closures.     

Intensity effects of the auditory evoked brain response to stimulus onset and cessation

Average evoked brain responses (EBR) to the onset (ON) and cessation (OFF) of 1-kHz pure-tone stimuli were computed from human scalp recordings. Stimuli of 2,000 msec duration were presented binaurally at 10 intensity levels. The waveform of the OFF EBR is similar to the ON EBR. The ON response is in general larger than the OFF response. Comparable ON and OFF amplitude response measures are both sensitive to changes in stimulus intensity which may be fit by a linear function. Significant differences in slope between ON and OFF amplitude intensity functions were demonstrated, which suggests different physiological systems for these responses.     

Pigeons respond to produce periods in which rewards are independent of responding

Pecks by pigeons on a response key produced an ON state during which intermittent rewards were freely available, i.e., independently of responding. Pecks during the ON state caused it to remain ON. If no pecks occurred, the state changed to OFF—the key color changed—and rewards were not presented. The state remained OFF until the next response. Thus, responses controlled the state in the chamber but did not cause immediate reinforcement. Four dimensions of the schedule were varied: the rates of response-independent rewards during ON; the duration of ON produced by each peck; the pattern of rewards during ON; and the presence vs absence of exteroceptive cues during ON and OFF. The results showed that rates of responding were primarily controlled by the duration of ON produced by each response. When each response caused a long period of ON, pecks occurred infrequently; when each response caused a brief period of ON, pecks were frequent.     

Auditory evoked brain responses: Comparison of ON and OFF responses at long and short durations

Average evoked brain responses (EBRs) to three durations of one kilohertz pure-tone stimuli were computed from human scalp recordings. Stimuli of 25, 75, and 2,000 msec duration were each presented binaurally at each of eight equally spaced intensity levels, ranging from 58 to 86 dB SPL. EBRs computed immediately following presentation, and immediately following removal of the 2,000-msec-duration stimulus result in ON and OFF responses, respectively. EBRs computed immediately following presentation of the 25- and 75-msec-duration stimuli appear to be the result of the sum of separate responses to stimulus onset and offset. Computer-dissected ON and OFF EBRs to short-duration stimuli are very similar in waveform and amplitude to the responses evoked by the onset and offset, respectively, of the 2,000-msec duration stimulus. Dissected ON and OFF responses demonstrate linear amplitude-intensity functions in amplitude ranges similar to respective ON and OFF responses to 2,000-msec stimulation. The data suggest that ON and OFF responses are mediated by independent physiological mechanisms.     

A simple LSI-11 system for real-time control,interevent time storage,and data analysis

A simple laboratory computer system based on a Digital Equipment Corporation LSI-11, floppy disk, DRV11 parallel input-output board, and the RT-11 operating system is described. Interface to experimental devices is provided through a lab-built relay driver and relay closure sensing interface. An extensive high-level software package provides an easy-to-use control language (e.g., stimuli can be controlled with a simple “TURN ON” or “TURN OFF” instruction) and easy-to-use FORTRAN subroutines for data exploration (e.g., “IFIND” searches a data file for a particular event). The control software automatically generates, codes, and stores a complete log of every input and output event and its time of occurrence in each of five simultaneously running experiments. This provides the capability to reanalyze data in light of hypotheses not available when the experiment was designed. The FORTRAN subroutine library for data exploration provides a conditional and iterative search facility to sift out events or sets of events from the data file for analysis. Standard FORTRAN statements perform arithmetic operations on the resulting data.     

Shrinkage of perceived tonal duration produced by extra sounds: effects of spectral density, temporal position, and transition direction

To investigate the mental mechanism that estimates the duration of sounds, the subjective duration of a tone was measured. In the first experiment a portion of the target sound was replaced with another sound. In the second and third experiments another sound either started or ended in the middle of the target sound. Ten or eleven undergraduates participated as listeners in each of the experiments. In the first experiment, effects of spectral spacing and those of temporal position of the replacing sound were tested. Compared with the intact case, the subjective duration of the replaced target shrunk, and the degree of shrinkage increased as the spectral spacing became wider. The temporal position of the replacing sound did not affect the degree of shrinkage. In the second experiment, effects produced by the start (ON) of the concurrent sound and those by the end (OFF) were compared. The ON case was more effective than the OFF case. In the third experiment, effects of the rise time and fall time of the concurrent sound were tested. A long rise and fall time reduced the difference between the ON and OFF cases. These results are discussed from two viewpoints, one assuming an interaction between the time markers, the other assuming continuous gate control in a neural-counting model for duration.     

The role of ON- and OFF-channel processing in the detection of bilateral symmetry

We present evidence that grouping for luminance does not take precedence over the detection of bilaterally symmetrical patterns. Using single-axis and double-axis images, we found that element pairs within which luminance is held constant drive symmetry-detection mechanisms more effectively than pairs within which luminance varies. Moreover, the performance decrement observed for patterns defined by element pairs within which luminance varies is not specific to interchannel variation. Luminance variation within the ON and OFF channels has the same effect as variation between the channels on the performance of axis-orientation identification tasks. It is argued that this constitutes possible evidence for subchannels within the ON and OFF channels. One of the characteristics of the subchannels is that each processes only a limited range of luminance steps. The implications of this type of luminance processing for the detection of symmetry in the visual scene are discussed.     

Evaluating the Acute Contributions of Dopaminergic Replacement to Gait With Obstacles in Parkinson's Disease

The influence of dopaminergic replacement (DR) on gait in people with Parkinson's disease (PD) is well documented. However, little is known about the acute effects of dopamine on more complex locomotor tasks that require visual guidance to avoid obstacles during gait. The authors investigated the influence of DR on locomotor behavior in a task where movement planning and control might be challenged by the height of the obstacle. The PD group included patients diagnosed with idiopathic PD (n = 12), as well as healthy controls (n = 12). Patients walked and stepped over obstacles of different heights before (OFF) and after (ON) levodopa intake. Spatial adjustments were not modulated by DR, but the step time to perform these anticipatory gait adjustments was longer only in PD-OFF (compared with healthy controls) when approaching the highest obstacle, but not PD-ON. During the crossing phase, trail limb toe clearance of PD patients was shorter than healthy controls only during the OFF state. ON-OFF comparisons were significantly different only for the time to reach the lead foot clearance over the highest obstacle. In summary, DR partially improved movement slowness but did not directly affect movement amplitude of lower limb regulation in this gait task.     

A running wheel tachometer

A photocell-actuated tachometer for running wheels is described. The number of counts generated per revolution of the wheel is a function of the number of trip wires inserted in the hub of the wheel axle. The circuit is presented in configurations that actuate relay contact closures and as a direct driver of TTL logic.     

Modular solid state behavioral training system

A system of multifunction solid state modules to perform most behavioral training schedules is described. The system takes advantage of integrated circuit size, speed, reliability, economy, and sophistication to overcome the problems inherent in relay systems. However, unlike other approaches with solid state units, knowledge of circuit design is not required. The usual complexity of changing from one program to another is reduced to the simplicity of turning a switch.     

Temporal characteristics of the surprise reaction induced by schema-discrepant visual and auditory events

Abstract

Two experiments investigated the effects of a schema-discrepant event on the surprise reaction. Schema-discrepancy concerned a physical feature of irrelevant distractor words that were presented while the subjects performed a choice reaction time task. The stimulus onset asynchrony (SOA) between the distractors and the task-relevant stimuli was manipulated in both experiments. The occurrence of the schema-discrepant event led to subjective feelings of surprise and enhanced recall of the stimulus material. In Experiment 1, the presentation of a schema-discrepant auditory event resulted in a pronounced increase of reaction time (RT) with a 0.2sec SOA but not with a 1.5sec SOA. In Experiment 2, the effects of both fixed and variable SOAs of four different lengths (simultaneous onset, 0.5sec, 1sec, or 2sec SOA) were investigated within a visual task context. The increase of RT was found to be most pronounced with SOAs of 0.5sec and lsec respectively, and more pronounced with variable than with fixed SOAs, especially with a simultaneous onset. These results provide information about the temporal characteristics of the inhibitory component of the surprise reaction, and suggest that the inhibitory effects of surprise depend considerably on the subjects' state of preparation for the experimental task.     

Impaired finger dexterity in Parkinson's disease is associated with praxis function

A controversial concept suggests that impaired finger dexterity in Parkinson’s disease may be related to limb kinetic apraxia that is not explained by elemental motor deficits such as bradykinesia. To explore the nature of dexterous difficulties, the aim of the present study was to assess the relationship of finger dexterity with ideomotor praxis function and parkinsonian symptoms. Twenty-five patients with Parkinson’s disease participated in the study. Their left and right arms were tested independently. Testing was done in an OFF and ON state as defined by a modified version of the Movement Disorder Society-Unified Parkinson’s Disease Rating Scale (MDS-UPDRS). Finger dexterity was assessed by a coin rotation (CR) task and ideomotor praxis using a novel test of upper limb apraxia (TULIA), in which the patients were requested to imitate and pantomime 48 meaningless, as well as communicative and tool-related gestures. Coin rotation significantly correlated with TULIA irrespective of the motor state and arm involved, but not with the MDS-UPDRS. This association was significantly influenced by Hoehn and Yahr stage.The strong association of finger dexterity with praxis function but not the parkinsonian symptoms indicates that impaired finger dexterity in Parkinson’s disease may be indeed apraxic in nature, yet, predominantly in advanced stages of the disease when cortical pathology is expected to develop. The findings are discussed within a cognitive-motor model of praxis function.     

Detection of stimulus change: The hypothetical roles of visual transient responses

Two random-dot patterns (D1 and D2) were displayed briefly in close temporal succession, separated by an interstimulus interval (ISI). The two patterns were identical except that D2 could contain one more element (addition) or one less element (subtraction) than D1. Observers were required to detect the addition or subtraction using a two-alternative forced-choice method. Three experiments were designed to examine Phillips and Singer’s (1974) suggestion that detection of additions and subtractions can be explained in terms of neural ON and OFF responses. Experiment 1 replicated Phillips and Singer’s finding that performance is progressively impaired as the ISI is increased. In Experiment 2, sudden shifts in luminance between D1 and D2 were combined with several durations of ISI to produce transient responses in a novel manner. Experiment 3 explored the roles of transient neural responses and of configurational changes as determinants of performance. Most predictions based on Phillips and Singer’s model were confirmed by the experimental outcomes. Some discrepancies between theory and data are noted, and directions for further research are suggested.     

Concomitant Pavlovian conditioning of heart rate and leg flexion responses in the rat

Pavlovian conditioning was studied in male Fischer 344 rats using tones as the conditioned stimulus (CS) and footshock as the unconditioned stimulus (UCS). Different groups of animals received (a) contiguous CS-UCS pairings with a 0.5 sec CS, (b) contiguous CS-UCS pairings with a 4.0 sec CS, or (c) a random sequence of noncontiguous tones and shocks using either a 0.5 sec or a 4.0 sec CS. Heart rate (HR) and leg flexion (LF) responses were recorded. Leg flexion conditioning occurred only in the 0.5 sec contiguous group. Decelerative HR CRs occurred only in the 4.0 sec contiguous group. Accelerative HR changes occurred in the other two groups but were significantly greater in the 0.5 sec contiguous group. These results are similar to but not identical to those obtained during eyeblink or nictitating membrane conditioning in rabbits, and suggest that the topography of the Pavlovian HR CR is dependent on the simultaneous occurrence of other classically conditioned responses.     

Which is more critical in identification of random figures,endpoints or closures?1

The present study intended to examine the criticality of the presence of endpoints and its complementary state, the presence of closures, in early figural identification. Three experiments used a same/different judgment task for simultaneously presented pairs of random figures. Rigorous control over the selections of stimulus figures containing closures and endpoints was ensured. Latencies predicted by six explanations of figural identification (i.e. parallel and the presence of endpoint detection; parallel and closure detection; serial, exhaustive and endpoint detection; serial, exhaustive and closure detection; serial, self‐terminating and endpoint detection; and serial, self‐terminating and closure detection) were evaluated by the obtained patterns of latencies. The experiments persistently indicated that serial, self‐terminating feature detections were executed as the means of the identification. Experiments 1 and 2 showed that closures were detected faster than endpoints. Experiment 3 further suggested that multiple closures were detected faster than a single closure.     

Scintillating lustre and brightness induced by radial lines

Gray disks inserted into the central gaps of an Ehrenstein pattern appear to lighten up and scintillate with each movement of the eye or stimulus pattern. We call this phenomenon scintillating lustre. Both phenomena-illusory brightness and scintillating lustre-depend on the presence of the radial inducing lines converging onto the gaps. Without the radii the gray disks appear matte. Using parametric stimulus variation, we show that the strength of scintillating lustre covaries with line-induced brightness enhancement when the length, width, number, and contrast of the radial lines, as well as the size of the gaps in the Ehrenstein figure, are varied. Following the proposal by Anstis (2000, Vision Research 40 2551-2556), we suggest that lustre results from a competition between the ON and OFF visual pathways. Whereas Helmholtz's binocular gloss is elicited by stereoscopically fused incremental and decremental stimuli, the present study demonstrates that lustre can also arise from the interaction between line-induced brightness (illusory increment) and a dark gray disk (physical decrement).     

UCS duration and conditioned suppression: Acquisition and extinction between-groups and terminal performance within-subjects

Two experiments demonstrated a positive monotonic relation between UCS duration and conditioned suppression ranging from no suppression at 0.05 sec to nearly complete suppression at 3.0 sec. In Exp 1, 5 acquisition groups were run at 0.5 mA. No suppression occurred at the shortest duration, approximately 50% suppression by Session 3 in two intermediate groups (0.2 and 0.5 sec) and nearly complete suppression by Session 3 at the two longest durations (1.0 and 3.0 sec). The relation between UCS duration and recovery of responding during extinction followed a parallel pattern. In Exp 2, terminal performance was studied within-subjects and the same relation was replicated.