Auditory short-term memory persistence for tonal signals in a songbird

Executive Functions in Birds

Executive functions comprise of top-down cognitive processes that exert control over information processing, from acquiring information to issuing a behavioral response. These cognitive processes of inhibition, working memory, and cognitive flexibility underpin complex cognitive skills, such as episodic memory and planning, which have been repeatedly investigated in several bird species in recent decades. Until recently, avian executive functions were studied in relatively few bird species but have gained traction in comparative cognitive research following MacLean and colleagues’ large-scale study from 2014. Therefore, in this review paper, the relevant previous findings are collected and organized to facilitate further investigations of these core cognitive processes in birds. This review can assist in integrating findings from avian and mammalian cognitive research and further the current understanding of executive functions’ significance and evolution.

Categorical Auditory Working Memory in Crows

The ability to group sensory data into behaviorally meaningful classes and to maintain these perceptual categories active in working memory is key to intelligent behavior. Here, we show that carrion crows, highly vocal and cognitively advanced corvid songbirds, possess categorical auditory working memory. The crows were trained in a delayed match-to-category task that required them to flexibly match remembered sounds based on the upward or downward shift of the sounds' frequency modulation. After training, the crows instantaneously classified novel sounds into the correct auditory categories. The crows showed sharp category boundaries as a function of the relative frequency interval of the modulation. In addition, the crows generalized frequency-modulated sounds within a category and correctly classified novel sounds kept in working memory irrespective of other acoustic features of the sound. This suggests that crows can form and actively memorize auditory perceptual categories in the service of cognitive control of their goal-directed behaviors.

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Crows performed a delayed match-to-category task with frequency modulated sounds

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Crows classified novel sounds into upward or downward modulated sound categories

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Crows showed sharp category boundaries and within-category generalization

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Crows can actively memorize auditory perceptual categories for cognitive control

Relative salience of spectral and temporal features in auditory long-term memory

In order to explore the representation of sound features in auditory long-term memory, two groups of ferrets were trained on Go vs Nogo, 3-zone classification tasks. The sound stimuli differed primarily along the spectral and temporal dimensions. In Group 1, two ferrets were trained to (i) classify tones based on their frequency (Tone-task), and subsequently learned to (ii) classify white noise based on its amplitude modulation rate (AM-task). In Group 2, two ferrets were trained to classify tones based on correlated combinations of their frequency and AM rate (AM-Tone task). Both groups of ferrets learned their tasks and were able to generalize performance along the trained spectral (tone frequency) or temporal (AM rate) dimensions. Insights into stimulus representations in memory were gained when the animals were tested with a diverse set of untrained probes that mixed features from the two dimensions. Animals exhibited a complex pattern of responses to the probes reflecting primarily the probes' spectral similarity with the training stimuli, and secondarily the temporal features of the stimuli. These diverse behavioral decisions could be well accounted for by a nearest-neighbor classifier model that relied on a multiscale spectrotemporal cortical representation of the training and probe sounds.

Scene analysis in the natural environment

The problem of scene analysis has been studied in a number of different fields over the past decades. These studies have led to important insights into problems of scene analysis, but not all of these insights are widely appreciated, and there remain critical shortcomings in current approaches that hinder further progress. Here we take the view that scene analysis is a universal problem solved by all animals, and that we can gain new insight by studying the problems that animals face in complex natural environments. In particular, the jumping spider, songbird, echolocating bat, and electric fish, all exhibit behaviors that require robust solutions to scene analysis problems encountered in the natural environment. By examining the behaviors of these seemingly disparate animals, we emerge with a framework for studying scene analysis comprising four essential properties: (1) the ability to solve ill-posed problems, (2) the ability to integrate and store information across time and modality, (3) efficient recovery and representation of 3D scene structure, and (4) the use of optimal motor actions for acquiring information to progress toward behavioral goals.

Receiver psychology turns 20: is it time for a broader approach?

Twenty years ago, a new conceptual paradigm known as 'receiver psychology' was introduced to explain the evolution of animal communication systems. This paradigm advanced the idea that psychological processes in the receiver's nervous system influence a signal's detectability, discriminability and memorability, and thereby serve as powerful sources of selection shaping signal design. While advancing our understanding of signal diversity, more recent studies make clear that receiver psychology, as a paradigm, has been structured too narrowly and does not incorporate many of the perceptual and cognitive processes of signal reception that operate between sensory transduction and a receiver's response. Consequently, the past two decades of research on receiver psychology have emphasized considerations of signal evolution but failed to ask key questions about the mechanisms of signal reception and their evolution. The primary aim of this essay is to advocate for a broader receiver psychology paradigm that more explicitly includes a research focus on receivers' psychological landscapes. We review recent experimental studies of hearing and sound communication to illustrate how considerations of several general perceptual and cognitive processes will facilitate future research on animal signalling systems. We also emphasize how a rigorous comparative approach to receiver psychology is critical to explicating the full range of perceptual and cognitive processes involved in receiving and responding to signals.

Effects of auditory recognition learning on the perception of vocal features in European starlings (Sturnus vulgaris)

Learning to recognize complex sensory signals can change the way they are perceived. European starlings (Sturnus vulgaris) recognize other starlings by their song, which consists of a series of complex, stereotyped motifs. Song recognition learning is accompanied by plasticity in secondary auditory areas, suggesting that perceptual learning is involved. Here, to investigate whether perceptual learning can be observed behaviorally, a same-different operant task was used to measure how starlings perceived small differences in motif structure. Birds trained to recognize conspecific songs were better at detecting variations in motifs from the songs they learned, even though this variation was not directly necessary to learn the associative task. Discrimination also improved as the reference stimulus was repeated multiple times. Perception of the much larger differences between different motifs was unaffected by training. These results indicate that sensory representations of motifs are enhanced when starlings learn to recognize songs.

Working memory for patterned sequences of auditory objects in a songbird

The capacity to remember sequences is critical to many behaviors, such as navigation and communication. Adult humans readily recall the serial order of auditory items, and this ability is commonly understood to support, in part, the speech processing for language comprehension. Theories of short-term serial recall posit either use of absolute (hierarchically structured) or relative (associatively structured) position information. To date, neither of these classes of theories has been tested in a comparative auditory model. European starlings, a species of songbird, use temporally structured acoustic signals to communicate, and thus have the potential to serve as a model system for auditory working memory. Here, we explore the strategies that starlings use to detect the serial order of ecologically valid acoustic communication signals and the limits on their capacities to do so. Using a two-alternative choice operant procedure, we demonstrate that starlings can attend to the serial ordering of at least four song elements (motifs) and can use this information to classify differently ordered sequences of motifs. Removing absolute position cues from sequences while leaving relative position cues intact, causes recognition to fail. We then show that starlings can, however, recognize motif-sequences using only relative position cues, but only under rigid circumstances. The data are consistent with a strong learning bias against relative position information, and suggest that recognition of structured vocal signals in this species is inherently hierarchical.

Auditory memory for temporal characteristics of sound

This study evaluates auditory memory for variations in the rate of sinusoidal amplitude modulation (SAM) of noise bursts in the European starling (Sturnus vulgaris). To estimate the extent of the starling's auditory short-term memory store, a delayed non-matching-to-sample paradigm was applied. The birds were trained to discriminate between a series of identical "sample stimuli" and a single "test stimulus". The birds classified SAM rates of sample and test stimuli as being either the same or different. Memory performance of the birds was measured as the percentage of correct classifications. Auditory memory persistence time was estimated as a function of the delay between sample and test stimuli. Memory performance was significantly affected by the delay between sample and test and by the number of sample stimuli presented before the test stimulus, but was not affected by the difference in SAM rate between sample and test stimuli. The individuals' auditory memory persistence times varied between 2 and 13 s. The starlings' auditory memory persistence in the present study for signals varying in the temporal domain was significantly shorter compared to that of a previous study (Zokoll et al. in J Acoust Soc Am 121:2842, 2007) applying tonal stimuli varying in the spectral domain.

Auditory memory: a comparison between humans and starlings

In this study, we compare the processing of acoustic signals in European starlings (Sturnus vulgaris) and in human listeners by observing the decay of short-term auditory memory in delayed non-matching-to-sample experiments. A series of identical "sample" stimuli and a final "test" stimulus were separated by variable delays (1 to 180.1 s). Subjects had to classify sample and test stimuli as being either the same or different. Test stimuli were pure tones that differed in a single signal feature, i.e., frequency, and song motifs that differed in multiple signal characteristics. We have tested several predictions concerning the memory performance of starlings and humans and we obtained the following outcome: (1) In contrast to our expectation, signal complexity had no effect. The overall analysis of the starling data did not show differences in memory performance for signals differing in single or multiple signal features. (2) Starling and human data supported the hypothesis that auditory memory impairs with increasing delay. This was also seen when interfering noise was added to the delay periods in an additional series with human subjects. (3) The starling data showed that the repetition of sample stimuli improved memory performance, compared to only a single presentation. Human memory performance, however, was similar for a single and for the repeated presentation of signals. (4) Differences in salience between sample and test stimuli were positively related to memory performance only for tonal stimuli but not for song motifs. Results are discussed with respect to a model based on signal detection theory and to requirements for the analysis of natural communication signals.