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The effect of deviations from temporal expectations on tempo discrimination was studied in 3 experiments using isochronous auditory sequences. Temporal deviations consisted of advancing or delaying the onset of a comparison pattern relative to an "expected" onset, defined by an extension of the periodicity of a preceding standard pattern. An effect of onset condition was most apparent when responses to faster and slower comparison patterns were analyzed separately and onset conditions were mixed. Under these conditions, early onsets produced more "faster" judgments and lower thresholds for tempo increases, and late onsets produced more "slower" judgments and lower thresholds for tempo decreases. In another experiment, pattern tempo had a similar effect: Fast tempos led to lower thresholds for tempo increases and slow tempos led to lower thresholds for tempo decreases. Findings support oscillator-based approaches to time discrimination.

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We describe the case of a 77-year-old man with asteroid hyalosis who had phacoemulsification and implantation of a plate-haptic intraocular lens (IOL). Intraoperatively, a tear occurred in the anterior capsule, and vision loss occurred 3 months after a neodymium:YAG posterior capsulotomy. Because of the asteroid hyalosis, a posteriorly dislocated IOL, which occurred after the capsulotomy, was difficult to diagnose. Careful retinoscopy established the aphakic condition of the eye, and the B-scan ultrasonography indicated the IOL's location.

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Recent research has shown that a single undrugged prior experience of the elevated plus-maze produces significant behavioural changes upon 24-h retest in rats and mice. Typically, when reexposed to the maze, animals display an increased avoidance of the open arms and a corresponding preference for the enclosed sections of the apparatus. Using ethological analyses, the present series of experiments sought to further characterize this phenomenon in mice and to determine whether or not it involves cholinergic receptor mechanisms. Results confirmed that behaviour during Trial 2 is markedly different to that seen on initial exposure, and that such changes are independent of the duration of Trial 1 (2 vs. 5 min). Retest behavioural changes included reduced entry latencies, reduced open arm entries, less time on the open arms and centre platform, lower levels of exploratory head-dipping, and increased entries into and time spent in the closed arms. The importance to the retest phenomenon of the first few minutes of initial exposure was further suggested by min-by-min analyses of the behaviour of animals naive to the maze. Results showed that behaviour during the first min is characterized by high levels of risk assessment from the centre platform and relatively low, but equal, levels of open- and closed-arm exploration. From min 2 onwards, however, behaviour showed a marked change with increasing open arm/centre platform avoidance, increasing closed-arm preference, and decreasing levels of risk assessment and exploratory head-dipping. Thus, it would appear that this within-session aversive learning transfers between sessions to account for behavioural profiles on retest. Irrespective of the duration of Trial 1 (2 or 5 min), posttrial administration of the muscarinic antagonist, scopolamine (0.1-1.0 mg/kg), failed to significantly alter the behavioural changes seen between trials. Data are discussed in relation to the apparent sensitization of fear produced by plus-maze exposure, its possible relation to phobia acquisition, and the need for further research on underlying mechanisms.

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The ability to detect frequency changes in transposed sequences of tones was examined in a series of seven experiments. Listeners were asked to judge which of two transposed (i.e., frequency-shifted) comparison patterns preserved the sequence of relative frequencies presented in a preceding standard pattern. The task was performed with five-tone and two-tone patterns under conditions of high and minimal pattern uncertainty. Regardless of pattern length or level of uncertainty, frequency discrimination thresholds for a change in the relative frequency of a single tone were considerably higher when patterns were transposed than when they were not. There was a tendency for performance to worsen with increasing degrees of transposition (primarily under high uncertainty) but most of the detrimental effects of transposition occurred within the first two semitones of transposition. Minimal uncertainty testing resulted in large improvements with five-tone patterns (as much as one order of magnitude), but there was no effect of level of uncertainty on performance with two-tone patterns. Thresholds for changes in two-tone patterns were similar to (although slightly higher than) those for five-tone patterns under minimal-uncertainty testing. This pattern of results reveals that the effects of stimulus complexity (sequence length) and pattern familiarity (level of uncertainty) on relative-frequency discrimination are quite similar to the effects of these variables on absolute-frequency discrimination.

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A principle of auditory perception that governs the detectability of changes in components in unfamiliar sequences of tones is demonstrated in four experiments. The proportion-of-the-total-duration (PTD) rule can be stated as follows: Each individual component of an unfamiliar sequence of tones is resolved with an accuracy that is a function of its proportion of the total duration of the sequence or "pattern." An adaptive-tracking frequency-discrimination task was used in all experiments. Experiment 1 demonstrated that the PTD rule holds over a wide range of total pattern durations, numbers of components, and component durations. Experiment 2 demonstrated that the PTD rule governs discrimination performance despite variation in the relative durations of context and target tones. Experiment 3, using a variable temporal position for the target, confirmed that the PTD effect does not require that a listener be able to anticipate the temporal location of the target tone. Experiment 4, using two target tones, showed that the PTD rules applies to the proportional duration of individual components within patterns and not to the total proportional duration of nonadjacent components within the pattern. These findings are incompatible with performance limitations based on a fixed-duration short-term memory capacity and with versions of informational limitations in which the amount of information in a pattern varies either with the number of components or with the total pattern duration. The PTD rule appears to reflect the way listeners distribute their attention when presented with unfamiliar complex sounds that have no structural properties (other than proportional duration) that significantly increase the salience of individual components.

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In three experiments, listeners' abilities to detect changes in randomly generated tonal sequences were determined for sequences or "patterns" ranging in total duration from 62.5 ms to 2 s. Experiment 1 utilized an adaptive-tracking procedure, with n, the number of pattern components, as the dependent variable, and included a variety of spectral and temporal discrimination tasks with isochronous patterns. When the to-be-detected change was the only variation on a given dimension (e.g., the presence or location of a brief pause), patterns were discriminable when the absolute duration of the changed element, or pause, exceeded a critical value. However, when each pattern component varied on the dimension of the to-be-detected change (e.g., frequency), discriminability was strongly related to the number of tones in the pattern, and only weakly to the durations of either the target components or the total pattern. This dependence of discrimination performance on n was also demonstrated with anisochronous patterns in experiment 2. Experiment 3 revealed the same dependence of performance on the number of components per pattern as did experiments 1 and 2, but with delta f/f as the dependent variable, rather than n. The number of pattern components and the proportional duration of the target components, relative to total pattern duration, were confounded in these experiments. Additional research is therefore required to determine whether number or proportional target-tone duration is the primary determinant of pattern discriminability.

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Three experiments demonstrated that the pattern of changes in articulatory rate in a precursor phrase can affect the perception of voicing in a syllable-initial prestress velar stop consonant. Fast and slow versions of a 10-word precursor phrase were recorded, and sections from each version were combined to produce several precursors with different patterns of change in articulatory rate. Listeners judged the identity of a target syllable, selected from a 7-member /gi/-ki/ voice-onset-time (VOT) continuum, that followed each precursor phrase after a variable brief pause. The major results were: (a) articulatory-rate effects were not restricted to the target syllable's immediate context; (b) rate effects depended on the pattern of rate changes in the precursor and not the amount of fast or slow speech or the proximity of fast or slow speech to the target syllable: and (c) shortening of the pause (or closure) duration led to a shortening of VOT boundaries rather than a lengthening as previously found in this phonetic context. Results are explained in terms of the role of dynamic temporal expectancies in determining the response to temporal information in speech, and implications for theories of extrinsic vs. intrinsic timing are discussed.

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In three experiments, subjects attended to one of two simultaneous nine-digit sequences, presented binaurally in different voices (one male, one female). Substantial repetition effects (defined as gains in immediate memory performance for previously presented sequences relative to novel ones) were found for two exposure conditions: (a) one that required reproduction of the full sequence on each exposure (Experiment 1), and (b) one that required recall of a different two-digit subsequence on each exposure (Experiment 2). In Experiment 3, the following conditions produced no repetition effects, even though tests had substantial power to detect small effects: 10 consecutive presentations in the unattended voice; 4 prior presentations in a task that required attention to each digit as it was presented (but not to digit order); and 4 prior presentations in a task that required attention to digit order during their presentations. These results, together with those of previous studies, support the conclusion that repetition effects on immediate memory occur only with procedures that encourage covert rehearsal of full-sequence order on each exposure. These findings also limit the generality of others' conclusions that event order is automatically encoded for attended events, and extend previous findings showing unattended exposures to be without effect on recall measures.

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