Implicit memory for words presented in short texts is preserved in Alzheimer's disease.

BACKGROUND: The level of efficiency of implicit memory in Alzheimer's disease remains unclear as previous studies using stem completion tasks have led to contradictory results. METHOD: The present study used target words embedded in significant short texts that subjects were required to read aloud (i.e. to enhance semantic processing). Texts were presented in two perceptual situations: 'simple' (blank spaces delimitating words) and complex' (spaces were filled by '8's). In the completion phase, patients had to write the first word that came to mind in order to complete a three-letter stem. The recognition phase explored explicit memory performance. The performance of 24 Alzheimer patients was compared to a matched sample of healthy controls. RESULTS: Reading times differed between groups and were shorter for healthy controls. Recognition was dramatically lower in patients, thus confirming the alteration of explicit memory in this pathology. However, a significant priming effect (e.g. the tendency to complete the stem with the aid of a previously explored word) was present in both groups and did not differ between patients and healthy controls. CONCLUSIONS: The absence of a correlation between priming and recognition scores suggests that this result cannot be explained by an explicit memory bias. Moreover, as the priming level was identical whatever the perceptual aspect of the text, we suggest that the priming effect is not only mediated by perceptual processes but also by lexical and conceptual processes, which to some extent are preserved during the light and moderate stages of this disease.

Measurement of the temporal-modulation transfer function for a single listener with cochlear hearing loss and left-hemisphere damage.

The modulation depth required for the detection of sinusoidal amplitude-modulation applied to a white noise carrier was measured as a function of modulation frequency, giving temporal modulation transfer functions (TMTFs). Five adult listeners with normal hearing (mean age 52 years), five elderly listeners with moderate cochlear hearing loss (mean age 66 years) and a single elderly listener (aged 73 years) with moderate cochlear hearing loss and left-hemisphere damage were tested in the right ear at 50 dB SL. The five elderly listeners were matched in audiogram with the brain-damaged listener. Modulation detection was systematically poorer than normal in the five elderly listeners with cochlear hearing loss. However, their TMTFs were lowpass in shape, as for the five normal-hearing adult listeners. Modulation detection was much poorer in the elderly listener with cochlear hearing loss and left-hemisphere damage compared to the five normal-hearing adults and the five elderly listeners with cochlear hearing loss. Moreover, modulation detection was poorer at 4, 64 and 128 Hz than at 8, 16 and 32 Hz in the brain-damaged listener, giving his TMTF a bandpass appearance. These results are in agreement with the hypothesis that the main factors limiting the ability to detect changes in the temporal-envelope of sounds are located at a central (retro-cochlear) level of the auditory system rather than at a peripheral (cochlear) level. They also suggest that the TMTF approach may prove useful in distinguishing peripheral and central hearing losses.

Assessing attentional control of breathing by reaction time.

The reaction time (RT) to an auditory stimulus was measured in 27 subjects during spontaneous breathing and during controlled breathing, which consisted of maintaining a set inspiratory duration. During spontaneous breathing, reaction times were unrelated to the time the stimulus was delivered during the breathing cycle. During controlled breathing, reaction times were longer than during spontaneous breathing. Peak reaction times were observed at the transition from inspiration to expiration. After the end of controlled breathing, reaction times gradually became shorter until they reached their initial level. The findings are discussed in terms of varying allocation of attentional resources to breathing. It is argued that probe RT methodology provides a suitable means for investigating attentional control of breathing.

Synchronization and knowledge of results in a ventilatory motor task.

The ability of healthy subjects to adopt a given value of inspiratory duration (TI) was examined in two different conditions: a knowledge condition in which subjects were informed of their performance on TI and synchronization of subjects' breathing rate to a periodic visual signal. The target value of TI was computed individually, by the same formula for all subjects in both procedures. 40 subjects were tested in a double-transfer design; each subject participated in two sessions 24 hr. apart. In addition to previous results showing better retention of the ventilatory task in subjects following the knowledge procedure after 24 hr., this study also shows better performance in this condition. No transfer could be evidenced, suggesting low similarity between the two tasks in spite of the fact that the resulting breathing patterns were nearly identical. The influence of the magnitude of the target on performance was also investigated.