Implicit Learning of Temporal Discriminations in Perception

We measured the temporal accuracy of signal transfer in the brain by means of periodic pulse stimuli in various sensory modalities using an adaptive threshold algorithm. Trains of supra-threshold signal pairs in 0° or 180° phase shifts appeared, and the subject indicated whether the signals of each pair in a train were simultaneous or not at various nominal frequencies of the pairs. The signals were spatially separate flashes of light, clicks, tactile pulses, or combinations thereof in intermodal comparisons. Temporal discrimination thresholds involving one signal in central photopic vision and the other in audition or tactile presentation to the finger tips did not exceed frequencies from 3 to 8 Hz, and in vision alone the average synchronism thresholds were about 10 Hz (SOA 0.05 s with 0.008 s pulses). The practice derived from 9 experimental sessions during 6 weeks improved temporal accuracy by factors ranging from 1.2 to 2.0 on the average in a sample of 33 naive subjects (university students), although no explicit feedback was given. The practice effect was lasting, for the average performance decrement was only 9% in 7 months. Thus, a considerable temporal modifiability must exist in the brain because a large learning effect was found in the simple temporal synchronism discrimination tasks.

The role of matching menstrual data with hormonal measurements in evaluating effectiveness of postcoital contraception

The effectiveness of postcoital contraception can only be estimated. The most commonly used method of calculation compares the expected pregnancy rate in the exposed population to the resultant pregnancies after treatment. Estimation of the fertile period and the day of ovulation are critical to calculate the expected pregnancies. The aim of this study was to improve the accuracy of calculations by evaluating the hormonal status on the day of contraceptive treatment. A total of 483 consecutive women requesting postcoital contraception was included in a prospective observational trial. A blood sample was obtained at the moment of consultation to measure serum luteinizing hormone, estradiol, and progesterone concentrations. An ethinylestradiol-levonorgestrel combination (100 micrograms/500 mg for two doses, 12 h apart) was then prescribed. The fertile period was estimated according to previous hormonal studies in the normal cycling population. Of 483 women, 64 (13.25%) women were excluded because they presented irregular menstrual cycles and 37 (7.6%) women were lost to follow-up. Two pregnancies occurred in the remaining 382 women. Following Wilcox's and Trussell's methods, 21.1 and 17.75 pregnancies should be expected, yielding an overall treatment effectiveness of 90.52% (95% confidence interval [CI] 62.58%-97.6%) and 88.73% (95% CI 55.93%-97.12%), respectively. Hormonal data were available in 356 women; 303 of whom presented with regular cycles. Hormonal information in this group restricted the number of exposed cases to 88 women. Of the women included in Trussell's method of analysis, only 51 (51.5%; p < 0.05) were at risk using hormonal data. Fifty-six percent (95% CI 34.9%-75.6%) of women with luteinizing hormone levels > 20 IU/L were not between days-1 and +1 of the cycle. Hormonal studies suggest that methods based on pregnancy risk calculated by cycle day do not faithfully reflect the real exposure.

Safety and effectiveness of hormonal postcoital contraception: a prospective study

OBJECTIVE

The aim of this study was to evaluate the demographic characteristics of the population attending our hospital requesting postcoital contraception and to determine the effectiveness of the method and its side-effects.

METHODS

A total of 503 women asking for postcoital contraception were included in a prospective open trial. After filling in a questionnaire dealing with demographic and contraceptive data, we prescribed an ethinylestradiol-levonorgestrel combination (100 micrograms/500 mg for two doses 12 h apart).

RESULTS

Only 487 women were available for analysis of demographic data. A further 77 were excluded because they presented irregular menstrual cycles and 55 cases were lost for follow-up. Mean age was 22.6 +/- 5.25 years and 35.9% of cases came to the center within the first 5 h after unprotected intercourse. Only 18.8% had previously asked for postcoital contraception. Breakage of condom was the most common reason for request (81.9%). Two pregnancies occurred in the remaining 355 women. According to Dixon's method 15.5 pregnancies should be expected being the overall efficacy of 87.14%. There were no serious adverse effects. Nausea and vomiting (16.33%) were the most prevalent and 59% of the users menstruated at the expected time whilst menses were delayed in 6% of the cases.

CONCLUSION

The combination of ethinylestradiol and levonorgestrel in low doses is an effective and safe method of postcoital contraception.