Biosonar dynamics and spatial attention in an unpredictable virtual localization task

Echolocating big brown bats hunt insects flying along unpredictable paths in front of vegetation. We conducted three psychophysical experiments to investigate how these bats alter their spatial attention when localizing virtual target echoes appearing unpredictably in azimuth and against weak physical clutter. Four bats were trained to detect virtual echoes presented from a 120 deg azimuthal array of six loudspeakers. Within a single trial, echoes could remain in the same position or shift unpredictably to a new one. The bats performed well in stationary trials but were less accurate when targets shifted more peripherally and contralaterally to the original azimuth. They aimed their sonar beams accurately at targets appearing centrally; they were less precise but faster when localizing targets in the periphery, maintaining a more central acoustic gaze with only momentary peripheral shifts. When localizing a shifted target, bats reduced the interpulse intervals between broadcasts and emitted proportionally more sonar sound groups, suggesting increased perceived task difficulty. Weak clutter located closely behind the virtual target reduced accuracy in localizing target shifts, affected the speed of beam aim adjustment, and was associated with an increase in broadcast duration. Interpulse intervals and sonar sound groups were not strongly affected by clutter. Behavioral differences between bats showed the impact of individual problem-solving strategies. These findings demonstrate that the distribution of spatial attention is biased towards the center of the ensonified field of view and is influenced by weak background clutter.