Physical and acoustic sediment properties of sediment cores from the eastern equatorial Atlantic

To reconstruct the deep-water circulation for the last 3.5 Ma from deep-sea sediments of the eastern equatorial Atlantic, sea floor morphology, sub-bottom reflectors and the echo character have been mapped on the basis of 3.5 kHz records and sediment cores. Physical properties of sediments and synthetic seismograms derived from them enable us to decipher reflector sequences in environments of pelagic, current-resuspended and turbidity sedimentation. The individual reflectors originate from carbonate dissolution, hiatus, coarse sand layers and interferences. Those which are related to carbonate dissolution and hiatus provide evidence of water-mass boundaries by their distribution. Five phases of different deep-water circulation can be seen in the record of th elast 3.5 Ma, and these are related to climate history: 1. Between 3.7 Ma and 2.2 Ma a strong deep-water circulation indicates a northward flow of bottom water below 4200 m (AABW = Antarctic-Bottom Water) and a southward flow of deep-water above 4200 m (NADW = North-Atlantic Deep Water). 2. Between 1.6 and 1.4 Ma a southward flow of bottom water below 4500 m and a diminished southward flow above 4500 m can be detected. This water-mass geometry can be interpreted by an expansion of the NADW-masses and a displacement of the AABW-masses during the same time. 3. Since 1.4 Ma a northward flow of a bottom-water current developed again. This current flow created a leeside sediment ridge in the southern part of the Kane Gap and furrows in the northern part of it. 4. Between 400,000 and 200,000 yrs B. P. the oceanic and atmospheric circulation increased. The strengthened oceanic circulation caused and increase in carbonate dissolution, which is documented by a traceable reflector from 2800 m to 4500 m water depth. At the same time an increase of the atmospheric circulation caused a drastic rise in the pelagic sediment accumulation (> 100 %) through an intensification of upwelling. This runs parallel with a higher oceanic productivity in the northern equatorial divergence zone and an enhanced supply of fluvial and probably eolian sediments from the Senegal and Guinea. 5. Before 10,000 yrs B. P. an erosive northward flowing bottom-water current prevailed below 4500 m water depth. After 10,000 yrs B.P. the bottom-water flow was sluggish and non erosive.

The independent effects of attention and lead stimulus properties on the acoustic blink reflex

The effects of attention to a lead stimulus and of its sensory properties on modulation of the acoustic blink reflex were investigated. Participants performed a reaction time task cued by an acoustic or a visual lead stimulus. In Experiment 1, half the participants were presented with sustained lead stimuli. For the remainder, the lead stimulus was discrete and consisted of two brief presentations that marked the onset and offset of a stimulus-free interval. In Experiment 2, sustained lead stimuli were presented at a low or high intensity. The attentional demands of the task enhanced blink latency and magnitude modulation during acoustic and visual lead stimuli, with blink modulation being largest at a late point during the lead stimulus. Independent of the attentional effects, blink latency and magnitude modulation were larger during sustained than during discrete acoustic lead stimuli, whereas there was no difference for visual lead stimuli. Increases in the intensity of the lead stimulus enhanced blink modulation regardless of lead stimulus modality. Attention to a lead stimulus and the properties of the lead stimulus appear to have independent effects on blink reflex modulation.

Across-formant integration and speech intelligibility:effects of acoustic source properties in the presence and absence of a contralateral interferer

The role of source properties in across-formant integration was explored using three-formant (F1+F2+F3) analogues of natural sentences (targets). In experiment 1, F1+F3 were harmonic analogues (H1+H3) generated using a monotonous buzz source and second-order resonators; in experiment 2, F1+F3 were tonal analogues (T1+T3). F2 could take either form (H2 or T2). Target formants were always presented monaurally; the receiving ear was assigned randomly on each trial. In some conditions, only the target was present; in others, a competitor for F2 (F2C) was presented contralaterally. Buzz-excited or tonal competitors were created using the time-reversed frequency and amplitude contours of F2. Listeners must reject F2C to optimize keyword recognition. Whether or not a competitor was present, there was no effect of source mismatch between F1+F3 and F2. The impact of adding F2C was modest when it was tonal but large when it was harmonic, irrespective of whether F2C matched F1+F3. This pattern was maintained when harmonic and tonal counterparts were loudness-matched (experiment 3). Source type and competition, rather than acoustic similarity, governed the phonetic contribution of a formant. Contrary to earlier research using dichotic targets, requiring across-ear integration to optimize intelligibility, H2C was an equally effective informational masker for H2 as for T2.