Evolutionary loss of a signalling colour is linked to increased response to conspecific chemicals

Behavioural responses to communicative signals combine input from multiple sensory modalities and signal compensation theory predicts that evolutionary shifts in one sensory modality could impact the response to signals in other sensory modalities. Here, we conducted two types of field experiments with 11 species spread across the lizard genus Sceloporus to test the hypothesis that the loss of visual signal elements affects behavioural responses to a chemical signal (conspecific scents) or to a predominantly visual signal (a conspecific lizard), both of which are used in intraspecific communication. We found that three species that have independently lost a visual signal trait, a colourful belly patch, responded to conspecific scents with increased chemosensory behaviour compared to a chemical control, while species with the belly patch did not. However, most species, with and without the belly patch, responded to live conspecifics with increased visual displays of similar magnitude. While aggressive responses to visual stimuli are taxonomically widespread in Sceloporus , our results suggest that increased chemosensory response behaviour is linked to colour patch loss. Thus, interactions across sensory modalities could constrain the evolution of complex signalling phenotypes, thereby influencing signal diversity.

The influence of total base ink coverage on the uniformity of digital prints overprinted with pearlescent inks

Print uniformity is an important parameter that can determine perceived quality of a printed product. If the product is of low print uniformity, its quality is often regarded as non-satisfactory. In this work we were interested in the uniformity of electrophotography prints overprinted with inks containing pearlescent pigments. Our goal was to determine whether the overall print uniformity was influenced by the total base ink coverage i.e. the ink coverage of the printing substrate before pigments were applied to it. Hence, three scenarios were considered: when pearlescent inks were printed over the unprinted paper, previously printed grey, and black colour patch. Nine different types of pearlescent pigments, dispersed in a transparent ink vehicle, were screen printed over the paper and the previously printed patches of grey and black colour. The base colours were printed in electrophotography. The uniformity of prints obtained in such a manner was determined by calculating GLCM parameters that were shown to correlate well with human perception of uniformity. It was shown that overprinting the electrophotography prints with pearlescent inks significantly decreased the uniformity of prints with black base colour and slightly improved the uniformity of those with grey colour. When pearlescent inks were printed over the paper, the uniformity did not change significantly. Observing the print uniformity of overprinted samples, the best results were obtained when pearlescent inks were printed directly to the paper, following the cases when they were printed over the grey and black prints. It is therefore concluded that the total base ink coverage has significant effect on the uniformity of electrophotography prints overprinted with pearlescent inks. The results indicate poor adhesion of the ink vehicle used as a carrier for pearlescent pigments to electrophotographic toner.

Boundary Strength Analysis: Combining colour pattern geometry and coloured patch visual properties for use in predicting behaviour and fitness

Colour patterns are used by many species to make decisions that ultimately affect their Darwinian fitness. Colour patterns consist of a mosaic of patches that differ in geometry and visual properties. Although traditionally pattern geometry and colour patch visual properties are analysed separately, these components are likely to work together as a functional unit. Despite this, the combined effect of patch visual properties, patch geometry, and the effects of the patch boundaries on animal visual systems, behaviour and fitness are relatively unexplored. Here we describe Boundary Strength Analysis (BSA), a novel way to combine the geometry of the edges (boundaries among the patch classes) with the receptor noise estimate (ΔS) of the intensity of the edges. The method is based upon known properties of vertebrate and invertebrate retinas. The mean and SD of ΔS (mΔS, sΔS) of a colour pattern can be obtained by weighting each edge class ΔS by its length, separately for chromatic and achromatic ΔS. This assumes those colour patterns, or parts of the patterns used in signalling, with larger mΔS and sΔS are more stimulating and hence more salient to the viewers. BSA can be used to examine both colour patterns and visual backgrounds. BSA was successful in assessing the estimated conspicuousness of colour pattern variants in two species, guppies (Poecilia reticulata) and Gouldian finches (Erythrura gouldiae), both polymorphic for patch colour, luminance and geometry. The pattern difference between chromatic and achromatic edges in both species reveals the possibility that chromatic and achromatic edges could function differently. BSA can be applied to any colour pattern used in intraspecific and interspecific behaviour. Seven predictions and four questions about colour patterns are presented.

Does language proficiency modulate oculomotor control? Evidence from Hindi–English bilinguals

Though many previous studies have reported enhanced cognitive control in bilinguals, few have investigated if such control is modulated by language proficiency. Here, we examined the inhibitory control of high and low proficient Hindi–English bilinguals on an oculomotor Stroop task. Subjects were asked to make a saccade as fast as possible towards the appropriate colour patch among competitors and distractors suppressing an eye movement evoked by the meaning of the word. High proficient bilinguals quickly oriented their attention towards the correct colour patch while effectively controlling the Stroop interference compared with low proficient subjects, on both colour and direction words. High proficient bilinguals also had fewer saccadic errors and demonstrated overall faster saccadic latency on all trial types. The results provide strong evidence for enhanced oculomotor control in proficient bilinguals compared with the less proficient ones.

Covert orienting to the locations of targets and distractors: Effects on response channel activation in a flanker task

The role of covert orienting of attention in response channel activation was examined using the flanker interference and precueing paradigms. Four experiments assessed the influence of distractors on the discrimination of a target colour patch under cueing conditions (three with non-informative, exogenous cues and one with informative, endogenous cues) that modulated attention at the flanker or target locations. Across all of the experiments, the amount of interference generated by the distractors was not modulated by the facilitation and inhibition of return induced by spatial attention precues. These results are consistent with previous reports of patients with neglect, which demonstrated that flanker interference proceeds at unattended locations (Audet, Bub, & Lecours, 1991; Cohen, Ivry, Rafal, & Kohn, 1995), and they suggest that response channel activation can occur independently from spatial attention.

Saccadic Eye Movements and Dual-Task Interference

Four dual-task experiments required a speeded manual choice response to a tone in a close temporal proximity to a saccadic eye movement task. In Experiment 1, subjects made a saccade towards a single transient; in Experiment 2, a red and a green colour patch were presented to left and right, and the saccade was to which ever patch was the pre-specified target colour. There was some slowing of the eye movement, but neither task combination showed typical dual-task interference (the “psychological refractory effect”). However, more interference was observed when the direction of the saccade depended on whether a central colour patch was red or green, or when the saccade was directed towards the numerically higher of two large digits presented to the left and the right. Experiment 5 examined a vocal second task, for comparison. The findings might reflect the fact that eye movements can be directed by two separate brain systems–-the superior colliculus and the frontal eye fields; commands from the latter but not the former may be delayed by simultaneous unrelated sensorimotor tasks.