Big brown bats (Eptesicus fuscus) emit trains of brief, wideband frequency-modulated (FM) echolocation sounds and use echoes of these sounds to orient, find insects, and guide flight through vegetation. They are observed to emit sounds that alternate between short and long inter-pulse intervals (IPIs), forming sonar sound groups. The occurrence of these strobe groups has been linked to flight in cluttered acoustic environments, but how exactly bats use sonar sound groups to orient and navigate is still a mystery. Here, the production of sound groups during clutter navigation was examined. Controlled flight experiments were conducted where the proximity of the nearest obstacles was systematically decreased while the extended scene was kept constant. Four bats flew along a corridor of varying widths (100, 70, and 40 cm) bounded by rows of vertically hanging plastic chains while in-flight echolocation calls were recorded. Bats shortened their IPIs for more rapid spatial sampling and also grouped their sounds more tightly when flying in narrower corridors. Bats emitted echolocation calls with progressively shorter IPIs over the course of a flight, and began their flights by emitting shorter starting IPI calls when clutter was denser. The percentage of sound groups containing 3 or more calls increased with increasing clutter proximity. Moreover, IPI sequences having internal structure become more pronounced when corridor width narrows. A novel metric for analyzing the temporal organization of sound sequences was developed, and the results indicate that the time interval between echolocation calls depends heavily on the preceding time interval. The occurrence of specific IPI patterns were dependent upon clutter, which suggests that sonar sound grouping may be an adaptive strategy for coping with pulse-echo ambiguity in cluttered surroundings.

Improving mental health treatment seeking among racial/ethnic minority college students should involve decreasing treatment barriers, improving access to affordable options, providing flexible scheduling or time-limited options, and decreasing stigma.

This study examined whether rumination and certainty about pessimistic future-event predictions (P-Certainty) would mediate the relation between lifetime suicide attempt history and future suicidal ideation. Young adults, ages 18-25 (N = 143), with a suicide attempt history (n = 32) or no previous suicide attempt history (n = 111) at baseline, were followed up 2-3 years later and completed measures of rumination, depressive symptoms, hopelessness, suicidal ideation, and pessimistic future-event certainty. Lifetime suicide attempts at baseline were associated with higher suicidal ideation at follow up, and this relation was mediated by rumination and P-Certainty. Suicide attempters may be vulnerable to later ideation due to higher levels of rumination and also certainty in their pessimistic future expectations.