What is it like to be a lizard? Directed attention and the flow of sensory experience in lizards and birds

Abstract

While the content of subjective (personal) experience is inaccessible to external observers, behavioral proxies can frame the nature of that experience and suggest its cognitive requirements. Directed attention is widely recognized as a feature of animal awareness. This descriptive study used the frequency of gaze shifts in lizards and birds as an indicator of the rate at which the animals change the perceptual segmentation of their ongoing experience. Most lizards are solitary, with social interactions limited to territorial defense and mating. Many are sit-and-wait insectivores that intersperse active foraging with long periods of sedentary activity. Others actively seek encounters with prey, either randomly (teiids) or through strategies indicative of intelligent planning (varanids). Birds typically change the direction of their attention five times faster than lizards while displaying more behavioral complexity and variety. A number of interspecies differences among both lizards and birds were observed in this study, consistent with the view that subjective experience varies uniquely across lifestyles, ecology, and phylogeny. These differences constitute variations in the structure of perceptual experience and could serve as probes for investigating neural correlates of animal consciousness.

Keywords: awareness; consciousness; ethology; gaze duration; perception; phenomenology; proxy behavior.

Figure 1

Frequency of gaze shifts for all lizards and birds. Each point is the mean number of gaze shifts/min for every observational session in the study. The mean for all lizards differed significantly from the mean for all birds by Welch’s unpaired 1-tailed t-test (t = 2.66, df = 11.33, p = 0.011).

Figure 2

Frequency of gaze shifts for lizards observed in at least three sessions. Bars indicate means + SD, color coded for the taxonomic family or infraorder to which each species belongs. The striped whiptail was a statistical outlier with a probability exceeding 98%, based on the ROUT method of Motulsky and Brown (2006). With it excluded, the remaining species did not vary significantly from one another by a Kruskall-Wallace 1-way ANOVA (KW = 8.62; n = 6, p > 0.12), but the other clades each differed significantly (p < 0.0001) from the striped whiptail by a nested 1-way ANOVA with Dunnett’s correction for multiple comparisons.

Figure 3

Frequency of gaze shifts for birds observed in at least three sessions. Bars indicate means + SD, color coded for the taxonomic order to which each species belongs. The tanager was a statistical outlier with a probability exceeding 98%, based on the ROUT method of Motulsky and Brown (2006). The high rate of gaze shifts for the dove was not a statistical outlier, but a nested 1-way ANOVA with Dunnett’s correction for multiple comparisons showed it to differ significantly from that of the macaw (p = 0.0003), stork (p < 0.0001), eagle (p = 0.0002), penguin (p = 0.012), and goose (p = 0.0013).

Figure 4

Time course of gaze shifts for the (A) water monitor, (B) frilled lizard, (C) rhinoceros iguana, and (D) blue-tongued skink. Each line records minute-to-minute rates of gaze shifts by the same lizard in observational sessions on different days.

Figure 5

Time course of gaze shifts and tongue licks by the same water monitor on two different days. Minute-to-minute number of gaze shifts and tongue licks (counts/min) by the same lizard in observational sessions on (A) 19 June and (B) 5 July.

Figure 6

Time course of gaze shifts with corresponding behaviors during a single typical session for the (A) water monitor, (B) rhinoceros iguana, and (C) blue-tongued skink.

Figure 7

Time course of gaze shifts for the (A) tanager, (B) goose, (C) macaw, and (D) eagle. Each line records minute-to-minute rates of gaze shifts on different days by the same eagle and macaw but different tanagers and geese.

Figure 8

Time course of gaze shifts with corresponding behaviors during a single typical session for a (A) goose, (B) macaw, and (C) eagle.