Sensory processing delays measured with the eye-movement correlogram
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Visual Perception/physiology↗
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Why practice reduces dual-task interference
M. A. Van Selst, E. Ruthruff, and J. C. Johnston (1999) found that practice dramatically reduced dual-task interference in a Psychological Refractory Period (PRP) paradigm with 1 vocal response and 1 manual response. Results from 3 further experiments using the highly trained participants of M. A. Van Selst et al. (1999) support 4 main conclusions: (a) A processing bottleneck exists even after extensive practice; (b) the principal cause of the reduction in PRP interference with practice is shortening of Task 1 bottleneck stages; (c) a secondary cause is that 1 or more, but not all, of the Task 2 substages that are postponed before practice are not postponed after practice (i.e., become automatized); and (d) the extent of PRP reduction with practice depends on the modalities of the 2 responses. A control experiment with 2 manual response tasks showed less PRP reduction with practice than that found by Van Selst et al.
Auditory Perception/physiology↗
Awareness during drowsiness: dynamics and electrophysiological correlates
During drowsy periods, performance on tasks requiring continuous attention becomes intermittent. Previously, we have reported that during drowsy periods of intermittent performance, 7 of 10 participants performing an auditory detection task exhibited episodes of non-responding lasting about 18 s (Makeig & Jung, 1996). Further, the time patterns of these episodes were repeated precisely in subsequent sessions. The 18-s cycles were accompanied by counterbalanced power changes within two frequency bands in the vertex EEG (near 4 Hz and circa 40 Hz). In the present experiment, performance patterns and concurrent EEG spectra were examined in four participants performing a continuous visuomotor compensatory tracking task in 15-20 minute bouts during a 42-hour sleep deprivation study. During periods of good performance, participants made compensatory trackball movements about twice per second, attempting to keep a target disk near a central ring. Autocorrelations of time series representing the distance of the target disk from the ring centre showed that during periods of poor performance marked near-18-s cycles in performance again appeared. There were phases of poor or absent performance accompanied by an increase in EEG power that was largest at 3-4 Hz. These studies show that in drowsy humans, opening and closing of the gates of behavioural awareness is marked not by the appearance of (12-14 Hz) sleep spindles, but by prominent EEG amplitude changes in the low theta band. Further, both EEG and behavioural changes during drowsiness often exhibit stereotyped 18-s cycles.
Controlled Clinical Trial↗
Vestibular short latency responses to pulsed linear acceleration in unanesthetized animals
Linear acceleration transients were used to elicit vestibular compound action potentials in non-invasively prepared, unanesthetized animals for the first time (chicks, Gallus domesticus, n = 33). Responses were composed of a series of up to 8 dominant peaks occurring within 8 msec of the stimulus. Response amplitudes for 1.0 g stimulus ranged from 1 to 10 microV. A late, slow, triphasic, anesthesia-labile component was identified as a dominant response feature in unanesthetized animals. Amplitudes increased and latencies decreased as stimulus intensity was increased (MANOVA P less than 0.05). Linear regression slope ranges were: amplitudes = 1.0-5.0 microV/g; latencies = -300 to -1100 microseconds/g. Thresholds for single polarity stimuli (0.035 +/- 0.022 g, n = 11) were significantly lower than those of alternating polarity (0.074 +/- 0.028 g, n = 18, P less than 0.001). Bilateral labyrinthectomy eliminated responses whereas bilateral extirpation of cochleae did not significantly change response thresholds. Intense acoustic masking (100/104 dB SL) produced no effect in 2 animals, but did produce small to moderate effects on response amplitudes in 7 others. Changes were attributed to effects on vestibular end organs. Results of unilateral labyrinth blockade (tetrodotoxin) suggest that P1 and N1 preferentially reflect ipsilateral eighth nerve compound action potentials whereas components beyond approximately 2 msec reflect activity from vestibular neurons that depend on both labyrinths. The results demonstrate that short latency vestibular compound action potentials can be measured in unanesthetized, non-invasively prepared animals.
NASA Discipline Neuroscience↗
Conventional and cross-correlation brain-stem auditory evoked responses in the white leghorn chick: rate manipulations
Rate-dependent changes in the chick brain-stem auditory evoked response (BAER) using conventional averaging and a cross-correlation technique were investigated. Five 15- to 19-day-old white leghorn chicks were anesthetized with Chloropent. In each chick, the left ear was acoustically stimulated. Electrical pulses of 0.1-ms duration were shaped, attenuated, and passed through a current driver to an Etymotic ER-2 which was sealed in the ear canal. Electrical activity from stainless-steel electrodes was amplified, filtered (300-3000 Hz) and digitized at 20 kHz. Click levels included 70 and 90 dB peSPL. In each animal, conventional BAERs were obtained at rates ranging from 5 to 90 Hz. BAERs were also obtained using a cross-correlation technique involving pseudorandom pulse sequences called maximum length sequences (MLSs). The minimum time between pulses, called the minimum pulse interval (MPI), ranged from 0.5 to 6 ms. Two BAERs were obtained for each condition. Dependent variables included the latency and amplitude of the cochlear microphonic (CM), wave 2 and wave 3. BAERs were observed in all chicks, for all level by rate combinations for both conventional and MLS BAERs. There was no effect of click level or rate on the latency of the CM. The latency of waves 2 and 3 increased with decreasing click level and increasing rate. CM amplitude decreased with decreasing click level, but was not influenced by click rate for the 70 dB peSPL condition. For the 90 dB peSPL click, CM amplitude was uninfluenced by click rate for conventional averaging. For MLS BAERs, CM amplitude was similar to conventional averaging for longer MPIs.(ABSTRACT TRUNCATED AT 250 WORDS).
NASA Discipline Neuroscience↗
Gravitoinertial force magnitude and direction influence head-centric auditory localization
We measured the influence of gravitoinertial force (GIF) magnitude and direction on head-centric auditory localization to determine whether a true audiogravic illusion exists. In experiment 1, supine subjects adjusted computer-generated dichotic stimuli until they heard a fused sound straight ahead in the midsagittal plane of the head under a variety of GIF conditions generated in a slow-rotation room. The dichotic stimuli were constructed by convolving broadband noise with head-related transfer function pairs that model the acoustic filtering at the listener's ears. These stimuli give rise to the perception of externally localized sounds. When the GIF was increased from 1 to 2 g and rotated 60 degrees rightward relative to the head and body, subjects on average set an acoustic stimulus 7.3 degrees right of their head's median plane to hear it as straight ahead. When the GIF was doubled and rotated 60 degrees leftward, subjects set the sound 6.8 degrees leftward of baseline values to hear it as centered. In experiment 2, increasing the GIF in the median plane of the supine body to 2 g did not influence auditory localization. In experiment 3, tilts up to 75 degrees of the supine body relative to the normal 1 g GIF led to small shifts, 1--2 degrees, of auditory setting toward the up ear to maintain a head-centered sound localization. These results show that head-centric auditory localization is affected by azimuthal rotation and increase in magnitude of the GIF and demonstrate that an audiogravic illusion exists. Sound localization is shifted in the direction opposite GIF rotation by an amount related to the magnitude of the GIF and its angular deviation relative to the median plane.
NASA Discipline Neuroscience↗
Can practice eliminate the psychological refractory period effect?
Can people learn to perform two tasks at the same time without interference? To answer this question, the authors trained 6 participants for 36 sessions in a Psychological Refractory Period (PRP) experiment, where Task 1 required a speeded vocal response to an auditory stimulus and Task 2 required a speeded manual response to a visual stimulus. The large PRP effect found initially (353 ms in Session 1) shrank to only about 40 ms over the course of practice, disappearing entirely for 1 of the 6 participants. This reduction in the PRP effect with practice is considerably larger than has been previously reported. The obtained pattern of factor interactions between stimulus onset asynchrony and each of three task difficulty manipulations (Task 1 judgment difficulty, Task 2 stimulus contrast, and Task 2 mapping compatibility) supports a postponement (bottleneck) account of dual-task interference, both before and after practice.
Pitch Perception/physiology↗