Self-deception is widespread in humans even though it can lead to disastrous consequences such as... more Self-deception is widespread in humans even though it can lead to disastrous consequences such as airplane crashes and financial meltdowns. Why is this potentially harmful trait so common? A controversial theory proposes that self-deception evolved to facilitate the deception of others. We test this hypothesis in the real world and find support for it: Overconfident individuals are overrated by observers and underconfident individuals are judged by observers to be worse than they actually are. Our findings suggest that people may not always reward the more accomplished individual but rather the more self-deceived. Moreover, if overconfident individuals are more likely to be risk-prone then by promoting them we may be creating institutions, including banks and armies, which are more vulnerable to risk. Our results reveal practical solutions for assessing individuals that circumvent the influence of self-deception and can be implemented in a range of organizations including educational institutions.
Primates can analyse visual scenes extremely rapidly, making
accurate decisions for presentation ... more Primates can analyse visual scenes extremely rapidly, making accurate decisions for presentation times of only 20 ms. We asked whether bumblebees, despite having potentially more limited processing power, could similarly detect and discriminate visual patterns presented for durations of 100 ms or less. Bumblebees detected stimuli and discriminated between differently oriented and coloured stimuli when presented as briefly as 25 ms but failed to identify ecologically relevant shapes (predatory spiders on flowers) even when presented for 100 ms. This suggests an important difference between primate and insect visual processing, so that while primates can capture entire visual scenes ‘at a glance’, insects might have to rely on continuous online sampling of the world around them, using a process of active vision, which requires longer integration times.
Visual search is well studied in human psychology, but we know comparatively little about similar... more Visual search is well studied in human psychology, but we know comparatively little about similar capacities in non-human animals. It is sometimes assumed that animal visual search is restricted to a single target at a time. In bees, for example, this limitation has been evoked to explain flower constancy, the tendency of bees to specialise on a single flower type. Few studies, however, have investigated bee visual search for multiple target types after extended learning and controlling for prior visual experience. We trained colour-naive bumblebees (Bombus terrestris) extensively in separate discrimination tasks to recognise two rewarding colours in interspersed block training sessions. We then tested them with the two colours simultaneously in the presence of distracting colours to examine whether and how quickly they were able to switch between the target colours. We found that bees switched between visual targets quickly and often. The median time taken to switch between targets was shorter than known estimates of how long traces last in bees' working memory, suggesting that their capacity to recall more than one learned target was not restricted by working memory limitations. Following our results, we propose a model of memory and learning that integrates our findings with those of previous studies investigating flower constancy.
Humans and other animals often communicate acoustically in noisy social groups, in which the back... more Humans and other animals often communicate acoustically in noisy social groups, in which the background noise generated by other individuals can mask signals of interest. When listening to speech in the presence of speech-like noise, humans experience a release from auditory masking when target and masker are spatially separated. We investigated spatial release from masking (SRM) in a free-field call recognition task in Cope’s gray treefrog (Hyla chrysoscelis). In this species, reproduction requires that females successfully detect, recognize, and localize a conspecific male in the noisy social environment of a breeding chorus. Using no-choice phonotaxis assays, we measured females’ signal recognition thresholds in response to a target signal (an advertisement call) in the presence and absence of chorus-shaped noise. Females experienced about 3 dB of masking release, compared with a co-localized condition, when the masker was displaced 90° in azimuth from the target. The magnitude of masking release was independent of the spectral composition of the target (carriers of 1.3 kHz, 2.6 kHz, or both). Our results indicate that frogs experience a modest degree of spatial unmasking when performing a call recognition task in the free-field, and suggest that variation in signal spectral content has small effects on both source identification and spatial unmasking. We discuss these results in the context of spatial unmasking in vertebrates and call recognition in frogs.
Vocal communication in crowded social environments is a difficult problem for both humans and non... more Vocal communication in crowded social environments is a difficult problem for both humans and nonhuman animals. Yet many important social behaviors require listeners to detect, recognize, and discriminate among signals in a complex acoustic milieu comprising the overlapping signals of multiple individuals, often of multiple species. Humans exploit a relatively small number of acoustic cues to segregate overlapping voices (as well as other mixtures of concurrent sounds, like polyphonic music). By comparison, we know little about how nonhuman animals are adapted to solve similar communication problems. One important cue enabling source segregation in human speech communication is that of frequency separation between concurrent voices: differences in frequency promote perceptual segregation of overlapping voices into separate “auditory streams” that can be followed through time. In this study, we show that frequency separation (ΔF) also enables frogs to segregate concurrent vocalizations, such as those routinely encountered in mixed-species breeding choruses. We presented female gray treefrogs (Hyla chrysoscelis) with a pulsed target signal (simulating an attractive conspecific call) in the presence of a continuous stream of distractor pulses (simulating an overlapping, unattractive heterospecific call). When the ΔF between target and distractor was small (e.g., ≤3 semitones), females exhibited low levels of responsiveness, indicating a failure to recognize the target as an attractive signal when the distractor had a similar frequency. Subjects became increasingly more responsive to the target, as indicated by shorter latencies for phonotaxis, as the ΔF between target and distractor increased (e.g., ΔF = 6–12 semitones). These results support the conclusion that gray treefrogs, like humans, can exploit frequency separation as a perceptual cue to segregate concurrent voices in noisy social environments. The ability of these frogs to segregate concurrent voices based on frequency separation may involve ancient hearing mechanisms for source segregation shared with humans and other vertebrates.
In this thesis, I characterise five species of the bushcricket genus Mecopoda with respect to the... more In this thesis, I characterise five species of the bushcricket genus Mecopoda with respect to their acoustic signals and morphology and investigate the phenomenon of acoustic synchrony in one of these five species: Mecopoda 'Chirper'. In several bushcricket species, individual ...
The precise timing of individual signals in response to those of signaling neighbors is seen in m... more The precise timing of individual signals in response to those of signaling neighbors is seen in many animal species. Synchrony is the most striking of the resultant timing patterns. One of the best examples of acoustic synchrony is in katydid choruses where males produce chirps with a high degree of temporal overlap. Cooperative hypotheses that speculate on the evolutionary origins of acoustic synchrony include the preservation of the species-specific call pattern, reduced predation risks, and increased call intensity. An alternative suggestion is that synchrony evolved as an epiphenomenon of competition between males in response to a female preference for chirps that lead other chirps. Previous models investigating the evolutionary origins of synchrony focused only on intrasexual competitive interactions. We investigated both competitive and cooperative hypotheses for the evolution of synchrony in the katydid Mecopoda “Chirper” using physiologically and ecologically realistic simulation models incorporating the natural variation in call features, ecology, female preferences, and spacing patterns, specifically aggregation. We found that although a female preference for leading chirps enables synchronous males to have some selective advantage, it is the female preference for the increased intensity of aggregations of synchronous males that enables synchrony to evolve as an evolutionarily stable strategy.
Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling... more Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling neighbours. In multi-male choruses, males that delay chirps in response to all their neighbours would remain silent most of the time and be unable to attract mates. This problem could be overcome if the afferent auditory system exhibited selective attention, and thus a male interacted only with a subset of neighbours. We investigated whether individuals of the bushcricket genus Mecopoda restricted their attention to louder chirps neurophysiologically, behaviourally and through spacing. We found that louder leading chirps were preferentially represented in the omega neuron but the representation of softer following chirps was not completely abolished. Following chirps that were 20 dB louder than leading chirps were better represented than leading chirps. During acoustic interactions, males synchronised with leading chirps even when the following chirps were 20 dB louder. Males did not restrict their attention to louder chirps during interactions but were affected by all chirps above a particular threshold. In the field, we found that males on average had only one or two neighbours whose calls were above this threshold. Selective attention is thus achieved in this bushcricket through spacing rather than neurophysiological filtering of softer signals.
Synchrony is a phenomenon that is seen in several rhythmically signalling animals including firef... more Synchrony is a phenomenon that is seen in several rhythmically signalling animals including fireflies, fiddler crabs (visual synchrony), frogs and katydids (acoustic synchrony). During acoustic interactions in katydids, synchrony is, however, imperfect and synchronous chirps typically lead or follow each other. In some katydid species, females have a strong preference for leading chirps, suggesting that consistent follower males would be at a disadvantage unless they used alternative strategies to attract females. In the katydid species Mecopoda ‘Chirper’ we used chirp period measurements to investigate whether individual males were consistent leaders and followers and whether followers could use three potentially advantageous strategies in field choruses: calling louder than leading males; spacing themselves such that they were either louder than leading males or were perceived to lead the leading males in some part of their acoustic range; and calling when leading males were silent. During acoustic interactions in choruses, three-fifths of the followers called more often when leaders were not calling. Leaders were, however, typically louder than followers but spacing enabled some quieter males to gain areas where they were the loudest among all males in a chorus. Chirp period and thus lead probability of males had low repeatability with no consistent leaders and followers across nights. Thus the disadvantage of being a follower in katydid choruses on a particular night could potentially be offset by solo calling or by the follower being a leader on other nights.
Five distinct song types of the genus Mecopoda were found in Southern India. Four were morphologi... more Five distinct song types of the genus Mecopoda were found in Southern India. Four were morphologically indistinguishable. Some of them were both sympatric and had synchronous breeding seasons. The songs of these five song types ranged from simple short chirps to highly complex songs with multiple components. The temporal patterns of the songs of the five song types were very distinctive, whereas their spectral features were similar. Component elements of the different songs were distinct despite overall similarity. The song types possibly represent sibling species.
Journal of Comparative Physiology A: …, Jan 1, 2007
In several bushcricket species, individual males synchronise their chirps during acoustic interac... more In several bushcricket species, individual males synchronise their chirps during acoustic interactions. Synchrony is imperfect with the chirps of one male leading or lagging the other by a few milliseconds. Imperfect synchrony is believed to have evolved in response to female preferences for leading chirps. We investigated the mechanism underlying synchrony in the bushcricket species Mecopoda ‘Chirper’ from Southern India using playback experiments and simulations of pairwise interactions. We also investigated whether intrinsic chirp period is a good predictor of leading probability during interactions between males. The mechanism underlying synchrony in this species differs from previously reported mechanisms in that it involves both a change in the oscillator’s intrinsic rate and resetting on a chirp-by-chirp basis. The form of the phase response curve differs from those of previously reported firefly and bushcricket species including the closely related Malaysian species Mecopoda elongata. Simulations exploring oscillator properties showed that the outcome of pairwise interactions was independent of initial phase and alternation was not possible. Solo intrinsic chirp period was a relatively good predictor of leading probability. However, changing the intrinsic period during interactions could enable males with longer periods to lead during acoustic interactions.
Self-deception is widespread in humans even though it can lead to disastrous consequences such as... more Self-deception is widespread in humans even though it can lead to disastrous consequences such as airplane crashes and financial meltdowns. Why is this potentially harmful trait so common? A controversial theory proposes that self-deception evolved to facilitate the deception of others. We test this hypothesis in the real world and find support for it: Overconfident individuals are overrated by observers and underconfident individuals are judged by observers to be worse than they actually are. Our findings suggest that people may not always reward the more accomplished individual but rather the more self-deceived. Moreover, if overconfident individuals are more likely to be risk-prone then by promoting them we may be creating institutions, including banks and armies, which are more vulnerable to risk. Our results reveal practical solutions for assessing individuals that circumvent the influence of self-deception and can be implemented in a range of organizations including educational institutions.
Primates can analyse visual scenes extremely rapidly, making
accurate decisions for presentation ... more Primates can analyse visual scenes extremely rapidly, making accurate decisions for presentation times of only 20 ms. We asked whether bumblebees, despite having potentially more limited processing power, could similarly detect and discriminate visual patterns presented for durations of 100 ms or less. Bumblebees detected stimuli and discriminated between differently oriented and coloured stimuli when presented as briefly as 25 ms but failed to identify ecologically relevant shapes (predatory spiders on flowers) even when presented for 100 ms. This suggests an important difference between primate and insect visual processing, so that while primates can capture entire visual scenes ‘at a glance’, insects might have to rely on continuous online sampling of the world around them, using a process of active vision, which requires longer integration times.
Visual search is well studied in human psychology, but we know comparatively little about similar... more Visual search is well studied in human psychology, but we know comparatively little about similar capacities in non-human animals. It is sometimes assumed that animal visual search is restricted to a single target at a time. In bees, for example, this limitation has been evoked to explain flower constancy, the tendency of bees to specialise on a single flower type. Few studies, however, have investigated bee visual search for multiple target types after extended learning and controlling for prior visual experience. We trained colour-naive bumblebees (Bombus terrestris) extensively in separate discrimination tasks to recognise two rewarding colours in interspersed block training sessions. We then tested them with the two colours simultaneously in the presence of distracting colours to examine whether and how quickly they were able to switch between the target colours. We found that bees switched between visual targets quickly and often. The median time taken to switch between targets was shorter than known estimates of how long traces last in bees' working memory, suggesting that their capacity to recall more than one learned target was not restricted by working memory limitations. Following our results, we propose a model of memory and learning that integrates our findings with those of previous studies investigating flower constancy.
Humans and other animals often communicate acoustically in noisy social groups, in which the back... more Humans and other animals often communicate acoustically in noisy social groups, in which the background noise generated by other individuals can mask signals of interest. When listening to speech in the presence of speech-like noise, humans experience a release from auditory masking when target and masker are spatially separated. We investigated spatial release from masking (SRM) in a free-field call recognition task in Cope’s gray treefrog (Hyla chrysoscelis). In this species, reproduction requires that females successfully detect, recognize, and localize a conspecific male in the noisy social environment of a breeding chorus. Using no-choice phonotaxis assays, we measured females’ signal recognition thresholds in response to a target signal (an advertisement call) in the presence and absence of chorus-shaped noise. Females experienced about 3 dB of masking release, compared with a co-localized condition, when the masker was displaced 90° in azimuth from the target. The magnitude of masking release was independent of the spectral composition of the target (carriers of 1.3 kHz, 2.6 kHz, or both). Our results indicate that frogs experience a modest degree of spatial unmasking when performing a call recognition task in the free-field, and suggest that variation in signal spectral content has small effects on both source identification and spatial unmasking. We discuss these results in the context of spatial unmasking in vertebrates and call recognition in frogs.
Vocal communication in crowded social environments is a difficult problem for both humans and non... more Vocal communication in crowded social environments is a difficult problem for both humans and nonhuman animals. Yet many important social behaviors require listeners to detect, recognize, and discriminate among signals in a complex acoustic milieu comprising the overlapping signals of multiple individuals, often of multiple species. Humans exploit a relatively small number of acoustic cues to segregate overlapping voices (as well as other mixtures of concurrent sounds, like polyphonic music). By comparison, we know little about how nonhuman animals are adapted to solve similar communication problems. One important cue enabling source segregation in human speech communication is that of frequency separation between concurrent voices: differences in frequency promote perceptual segregation of overlapping voices into separate “auditory streams” that can be followed through time. In this study, we show that frequency separation (ΔF) also enables frogs to segregate concurrent vocalizations, such as those routinely encountered in mixed-species breeding choruses. We presented female gray treefrogs (Hyla chrysoscelis) with a pulsed target signal (simulating an attractive conspecific call) in the presence of a continuous stream of distractor pulses (simulating an overlapping, unattractive heterospecific call). When the ΔF between target and distractor was small (e.g., ≤3 semitones), females exhibited low levels of responsiveness, indicating a failure to recognize the target as an attractive signal when the distractor had a similar frequency. Subjects became increasingly more responsive to the target, as indicated by shorter latencies for phonotaxis, as the ΔF between target and distractor increased (e.g., ΔF = 6–12 semitones). These results support the conclusion that gray treefrogs, like humans, can exploit frequency separation as a perceptual cue to segregate concurrent voices in noisy social environments. The ability of these frogs to segregate concurrent voices based on frequency separation may involve ancient hearing mechanisms for source segregation shared with humans and other vertebrates.
In this thesis, I characterise five species of the bushcricket genus Mecopoda with respect to the... more In this thesis, I characterise five species of the bushcricket genus Mecopoda with respect to their acoustic signals and morphology and investigate the phenomenon of acoustic synchrony in one of these five species: Mecopoda 'Chirper'. In several bushcricket species, individual ...
The precise timing of individual signals in response to those of signaling neighbors is seen in m... more The precise timing of individual signals in response to those of signaling neighbors is seen in many animal species. Synchrony is the most striking of the resultant timing patterns. One of the best examples of acoustic synchrony is in katydid choruses where males produce chirps with a high degree of temporal overlap. Cooperative hypotheses that speculate on the evolutionary origins of acoustic synchrony include the preservation of the species-specific call pattern, reduced predation risks, and increased call intensity. An alternative suggestion is that synchrony evolved as an epiphenomenon of competition between males in response to a female preference for chirps that lead other chirps. Previous models investigating the evolutionary origins of synchrony focused only on intrasexual competitive interactions. We investigated both competitive and cooperative hypotheses for the evolution of synchrony in the katydid Mecopoda “Chirper” using physiologically and ecologically realistic simulation models incorporating the natural variation in call features, ecology, female preferences, and spacing patterns, specifically aggregation. We found that although a female preference for leading chirps enables synchronous males to have some selective advantage, it is the female preference for the increased intensity of aggregations of synchronous males that enables synchrony to evolve as an evolutionarily stable strategy.
Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling... more Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling neighbours. In multi-male choruses, males that delay chirps in response to all their neighbours would remain silent most of the time and be unable to attract mates. This problem could be overcome if the afferent auditory system exhibited selective attention, and thus a male interacted only with a subset of neighbours. We investigated whether individuals of the bushcricket genus Mecopoda restricted their attention to louder chirps neurophysiologically, behaviourally and through spacing. We found that louder leading chirps were preferentially represented in the omega neuron but the representation of softer following chirps was not completely abolished. Following chirps that were 20 dB louder than leading chirps were better represented than leading chirps. During acoustic interactions, males synchronised with leading chirps even when the following chirps were 20 dB louder. Males did not restrict their attention to louder chirps during interactions but were affected by all chirps above a particular threshold. In the field, we found that males on average had only one or two neighbours whose calls were above this threshold. Selective attention is thus achieved in this bushcricket through spacing rather than neurophysiological filtering of softer signals.
Synchrony is a phenomenon that is seen in several rhythmically signalling animals including firef... more Synchrony is a phenomenon that is seen in several rhythmically signalling animals including fireflies, fiddler crabs (visual synchrony), frogs and katydids (acoustic synchrony). During acoustic interactions in katydids, synchrony is, however, imperfect and synchronous chirps typically lead or follow each other. In some katydid species, females have a strong preference for leading chirps, suggesting that consistent follower males would be at a disadvantage unless they used alternative strategies to attract females. In the katydid species Mecopoda ‘Chirper’ we used chirp period measurements to investigate whether individual males were consistent leaders and followers and whether followers could use three potentially advantageous strategies in field choruses: calling louder than leading males; spacing themselves such that they were either louder than leading males or were perceived to lead the leading males in some part of their acoustic range; and calling when leading males were silent. During acoustic interactions in choruses, three-fifths of the followers called more often when leaders were not calling. Leaders were, however, typically louder than followers but spacing enabled some quieter males to gain areas where they were the loudest among all males in a chorus. Chirp period and thus lead probability of males had low repeatability with no consistent leaders and followers across nights. Thus the disadvantage of being a follower in katydid choruses on a particular night could potentially be offset by solo calling or by the follower being a leader on other nights.
Five distinct song types of the genus Mecopoda were found in Southern India. Four were morphologi... more Five distinct song types of the genus Mecopoda were found in Southern India. Four were morphologically indistinguishable. Some of them were both sympatric and had synchronous breeding seasons. The songs of these five song types ranged from simple short chirps to highly complex songs with multiple components. The temporal patterns of the songs of the five song types were very distinctive, whereas their spectral features were similar. Component elements of the different songs were distinct despite overall similarity. The song types possibly represent sibling species.
Journal of Comparative Physiology A: …, Jan 1, 2007
In several bushcricket species, individual males synchronise their chirps during acoustic interac... more In several bushcricket species, individual males synchronise their chirps during acoustic interactions. Synchrony is imperfect with the chirps of one male leading or lagging the other by a few milliseconds. Imperfect synchrony is believed to have evolved in response to female preferences for leading chirps. We investigated the mechanism underlying synchrony in the bushcricket species Mecopoda ‘Chirper’ from Southern India using playback experiments and simulations of pairwise interactions. We also investigated whether intrinsic chirp period is a good predictor of leading probability during interactions between males. The mechanism underlying synchrony in this species differs from previously reported mechanisms in that it involves both a change in the oscillator’s intrinsic rate and resetting on a chirp-by-chirp basis. The form of the phase response curve differs from those of previously reported firefly and bushcricket species including the closely related Malaysian species Mecopoda elongata. Simulations exploring oscillator properties showed that the outcome of pairwise interactions was independent of initial phase and alternation was not possible. Solo intrinsic chirp period was a relatively good predictor of leading probability. However, changing the intrinsic period during interactions could enable males with longer periods to lead during acoustic interactions.
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financial meltdowns. Why is this potentially harmful trait so common? A controversial theory proposes that self-deception
evolved to facilitate the deception of others. We test this hypothesis in the real world and find support for it: Overconfident
individuals are overrated by observers and underconfident individuals are judged by observers to be worse than they
actually are. Our findings suggest that people may not always reward the more accomplished individual but rather the more
self-deceived. Moreover, if overconfident individuals are more likely to be risk-prone then by promoting them we may be
creating institutions, including banks and armies, which are more vulnerable to risk. Our results reveal practical solutions for
assessing individuals that circumvent the influence of self-deception and can be implemented in a range of organizations
including educational institutions.
accurate decisions for presentation times of only 20 ms. We asked
whether bumblebees, despite having potentially more limited
processing power, could similarly detect and discriminate visual
patterns presented for durations of 100 ms or less. Bumblebees
detected stimuli and discriminated between differently oriented and
coloured stimuli when presented as briefly as 25 ms but failed to
identify ecologically relevant shapes (predatory spiders on flowers)
even when presented for 100 ms. This suggests an important
difference between primate and insect visual processing, so that
while primates can capture entire visual scenes ‘at a glance’, insects
might have to rely on continuous online sampling of the world around
them, using a process of active vision, which requires longer
integration times.
financial meltdowns. Why is this potentially harmful trait so common? A controversial theory proposes that self-deception
evolved to facilitate the deception of others. We test this hypothesis in the real world and find support for it: Overconfident
individuals are overrated by observers and underconfident individuals are judged by observers to be worse than they
actually are. Our findings suggest that people may not always reward the more accomplished individual but rather the more
self-deceived. Moreover, if overconfident individuals are more likely to be risk-prone then by promoting them we may be
creating institutions, including banks and armies, which are more vulnerable to risk. Our results reveal practical solutions for
assessing individuals that circumvent the influence of self-deception and can be implemented in a range of organizations
including educational institutions.
accurate decisions for presentation times of only 20 ms. We asked
whether bumblebees, despite having potentially more limited
processing power, could similarly detect and discriminate visual
patterns presented for durations of 100 ms or less. Bumblebees
detected stimuli and discriminated between differently oriented and
coloured stimuli when presented as briefly as 25 ms but failed to
identify ecologically relevant shapes (predatory spiders on flowers)
even when presented for 100 ms. This suggests an important
difference between primate and insect visual processing, so that
while primates can capture entire visual scenes ‘at a glance’, insects
might have to rely on continuous online sampling of the world around
them, using a process of active vision, which requires longer
integration times.