Looming Effects on Attentional Modulation of Prepulse Inhibition Paradigm

In a hazardous environment, it is fundamentally important to successfully evaluate the motion of sounds. Previous studies demonstrated “auditory looming bias” in both macaques and humans, as looming sounds that increased in intensity were processed preferentially by the brain. In this study on rats, we used a prepulse inhibition (PPI) of the acoustic startle response paradigm to investigate whether auditory looming sound with intrinsic warning value could draw attention of the animals and dampen the startle reflex caused by the startling noise. We showed looming sound with a duration of 120 ms enhanced PPI compared with receding sound with the same duration; however, when both sound types were at shorter duration/higher change rate (i.e., 30 ms) or longer duration/lower rate (i.e., more than 160 ms), there was no PPI difference. This indicates that looming sound–induced PPI enhancement was duration dependent. We further showed that isolation rearing impaired the abilities of animals to differentiate looming and receding prepulse stimuli, although it did not abolish their discrimination between looming and stationary prepulse stimuli. This suggests that isolation rearing compromised their assessment of potential threats from approaching objects and receding objects.

Corticostriatal control of defense behavior in mice induced by auditory looming cues

Animals exhibit innate defense behaviors in response to approaching threats cued by the dynamics of sensory inputs of various modalities. The underlying neural circuits have been mostly studied in the visual system, but remain unclear for other modalities. Here, by utilizing sounds with increasing (vs. decreasing) loudness to mimic looming (vs. receding) objects, we find that looming sounds elicit stereotypical sequential defensive reactions: freezing followed by flight. Both behaviors require the activity of auditory cortex, in particular the sustained type of responses, but are differentially mediated by corticostriatal projections primarily innervating D2 neurons in the tail of the striatum and corticocollicular projections to the superior colliculus, respectively. The behavioral transition from freezing to flight can be attributed to the differential temporal dynamics of the striatal and collicular neurons in their responses to looming sound stimuli. Our results reveal an essential role of the striatum in the innate defense control.

A Vigilance Explanation of Musical Chills? Effects of Loudness and Brightness Manipulations

Recent research has suggested that low-level psychoacoustic parameters such as loudness and spectral brightness are correlated with musical chills, a subjective emotional experience accompanied by goosebumps, shivers, and tingling sensations. These relationships may be explained by a vigilance theory of chills, through the process of auditory looming; however, these correlations or theories have never been causally tested. In the current study, participants ( N = 40) listened to five variations (original, low loudness, high loudness, low brightness, high brightness) of an experimental and control piece of chills music, characterized by a crescendo and guitar solo respectively; this qualitative distinction was made based on whether the underlying musical structure of the pieces was or was not capable of engaging auditory looming processes. It was predicted that increases in loudness would result in increased chills frequency across participants, indicated by button presses; brightness was included as an exploratory parameter. Results show that for the experimental piece, increases in loudness resulted in significantly more frequent chills experiences, and increases in brightness significantly reduced the frequency of chills, whereas no effects were found for the control piece. Findings are discussed in terms of vigilance and social bonding theories of chills, and the complex interactions between low-level psychoacoustic properties and higher-level musical structures.

Asymmetries in behavioral and neural responses to spectral cues demonstrate the generality of auditory looming bias

Studies of auditory looming bias have shown that sources increasing in intensity are more salient than sources decreasing in intensity. Researchers have argued that listeners are more sensitive to approaching sounds compared with receding sounds, reflecting an evolutionary pressure. However, these studies only manipulated overall sound intensity; therefore, it is unclear whether looming bias is truly a perceptual bias for changes in source distance, or only in sound intensity. Here we demonstrate both behavioral and neural correlates of looming bias without manipulating overall sound intensity. In natural environments, the pinnae induce spectral cues that give rise to a sense of externalization; when spectral cues are unnatural, sounds are perceived as closer to the listener. We manipulated the contrast of individually tailored spectral cues to create sounds of similar intensity but different naturalness. We confirmed that sounds were perceived as approaching when spectral contrast decreased, and perceived as receding when spectral contrast increased. We measured behavior and electroencephalography while listeners judged motion direction. Behavioral responses showed a looming bias in that responses were more consistent for sounds perceived as approaching than for sounds perceived as receding. In a control experiment, looming bias disappeared when spectral contrast changes were discontinuous, suggesting that perceived motion in distance and not distance itself was driving the bias. Neurally, looming bias was reflected in an asymmetry of late event-related potentials associated with motion evaluation. Hence, both our behavioral and neural findings support a generalization of the auditory looming bias, representing a perceptual preference for approaching auditory objects.

Continuous subjective loudness responses to reversals and inversions of a sound recording of an orchestral excerpt

Twenty-four respondents continuously rated the loudness of the first 65 seconds of a Dvořák Slavonic Dance, which was known to vary considerably in loudness. They also rated the same excerpt when the sound file was digitally treated so that (1) the sound pressure level (SPL) was inverted or (2) it was temporally reversed or (3) both 1 and 2. Specifically we wanted to see if acoustic intensity was processed into the percept of loudness primarily using a bottom-up (indifferent to timbral environment and thematic cues) or top-down style (where musical context, such as instrument identity and musical expectation affects the loudness rating). Comparing the different versions (conditions) allowed us to ascertain which style they were likely to be using. A single, six-second region was located as being differentiated across two conditions, where loudness seemed to be increased due to expectation of the instrument and orchestral texture, despite the lower SPL. We named this effect an auditory loudness stroop. A second region was differentiated between the two conditions, but its explanation appears to involve two factors, auditory looming perception and the reversal of stimulus note ramps. The overall conclusion was that the predominant processing style for loudness rating was bottom-up. Implications for further research and application to models of loudness are discussed.