Experiments that have investigated navigation in insects add considerably to the generality of the arguments presented by Jeffery et al., in revealing additional evidence for potential bicoded processing in animal brains. A contemporary point of interest in neuroscience is whether solving complex cognitive problems actually requires large mammalian brains (Chittka & Niven Reference Chittka and Niven2009). In this regard, free-flying bees are an interesting model for understanding how visual systems deal with navigation in a three-dimensional world.
It is known that the mechanism by which both stingless bees (Melipona panamica) and honeybees (Apis mellifera) judge distance in the horizontal plane is visually driven by optical flow, where the velocity of angular image motion is integrated over time to enable a bee to estimate the flown distance with accuracy (Dacke & Srinivasan Reference Dacke and Srinivasan2007; Eckles et al. Reference Eckles, Roubik and Nieh2012). Interestingly, when honeybees are presented with the equivalent type of visual problem requiring judgment of distance using optic flow in the vertical plane, they solve this task with a much lower level of precision (Dacke & Srinivasan Reference Dacke and Srinivasan2007). We argue that the relative accuracy of navigation in the horizontal and vertical dimensions makes sense in terms of normal ecological imperatives, and that brain plasticity can be recruited to facilitate robust bicoded processing if required.
Studies on honeybees suggest that visual processing of optic flow is dominated by information impinging on the ventral visual field (Dacke & Srinivasan Reference Dacke and Srinivasan2007), which makes ecological sense for an animal that predominantly flies in the horizontal plane when foraging for nutrition. In contrast, the stingless bee operates in dense tropical environments where flower resources are typically scattered horizontally and throughout a range of vertical heights of up to 40 metres in the forest canopy. These stingless bees have been shown to be equally proficient at gauging distance in both the horizontal and vertical planes, potentially using optic flow mechanisms in both ventral and lateral visual fields (Eckles et al. Reference Eckles, Roubik and Nieh2012). Nonetheless, honeybees do sometimes also have to operate in complex three-dimensional environments such as tropical forests. How might they deal with the complexity of reliable orientation in the vertical plane? We suggest below that honeybees are able to use information other than optic flow, and that their brains can learn to combine different visual perceptions to solve novel problems, in a manner consistent with the bicoded hypothesis.
Whilst honeybees do communicate horizontal direction and distance to hive mates through a symbolic dance communication language, this does not reliably communicate elevation (Dacke & Srinivasan Reference Dacke and Srinivasan2007). It is therefore likely that individual foragers must learn through their own experience to determine vertical components of their three-dimensional world. One possible solution to this problem is relationship learning – estimating vertical position by understanding the relative relationships, such as above/below, between different elemental features in the environment. The capacity to process such relationship rules is not innate for a brain. Three-months-old human babies do not show evidence of relationship processing, although by 6 months of age this capacity has developed (Quinn et al. Reference Quinn, Polly, Furer, Dobson and Narter2002). Other adult primates, such as capuchin monkeys (Cebus apella), also show a capacity for solving problems requiring the learning of above/below rules (Spinozzi et al. Reference Spinozzi, Lubrano and Truppa2004). Recent work in honeybees shows that while their brains do not innately code spatial relationship rules, individual free-flying bees can learn such relationships through visual experience, including the reliable processing of above/below (Avarguès-Weber et al. Reference Avarguès-Weber, Dyer, Combe and Giurfa2012).
The relationship rule processing mechanism observed in honeybees would thus give the potential for experienced individuals to forage in complex environments with acquired knowledge about relative vertical positions between biologically plausible objects, such as flowers and tree limbs (Chittka & Jensen Reference Chittka and Jensen2011; Dyer et al. Reference Dyer, Rosa and Reser2008). Could “vertical knowledge” then be combined with the perception of optic flow in the horizontal plane, to give a true bicoded perception of three-dimensional space? We believe so. The work on how honeybees process complex visual relationship rules, including above/below and same/different, suggests that there is also a capacity to learn simultaneously two separate rules or types of visual information, and then combine this acquired knowledge to solve novel problems (Avarguès-Weber et al. Reference Avarguès-Weber, Dyer, Combe and Giurfa2012). Thus, although the honeybee appears to process horizontal and vertical optic flows as separate signals (Dacke & Srinivasan Reference Dacke and Srinivasan2007), it does appear that their brains have the capacity to combine multiple sources of sensory perception and other spatial cues to make novel decisions in complex environments.
In summary, learning to build concepts to process multiple dimensions of three-dimensional navigation using a bicoded system as hypothesised by Jeffery et al. may represent a more general biological capacity, which likely extends to relatively simple brains such as those of insects. Further, we suggest that the opportunity for a brain of an individual to learn complex tasks through experience is critical to revealing the true behavioural capabilities in animals, irrespective of the relative number of neurons and synapses involved.
Experiments that have investigated navigation in insects add considerably to the generality of the arguments presented by Jeffery et al., in revealing additional evidence for potential bicoded processing in animal brains. A contemporary point of interest in neuroscience is whether solving complex cognitive problems actually requires large mammalian brains (Chittka & Niven Reference Chittka and Niven2009). In this regard, free-flying bees are an interesting model for understanding how visual systems deal with navigation in a three-dimensional world.
It is known that the mechanism by which both stingless bees (Melipona panamica) and honeybees (Apis mellifera) judge distance in the horizontal plane is visually driven by optical flow, where the velocity of angular image motion is integrated over time to enable a bee to estimate the flown distance with accuracy (Dacke & Srinivasan Reference Dacke and Srinivasan2007; Eckles et al. Reference Eckles, Roubik and Nieh2012). Interestingly, when honeybees are presented with the equivalent type of visual problem requiring judgment of distance using optic flow in the vertical plane, they solve this task with a much lower level of precision (Dacke & Srinivasan Reference Dacke and Srinivasan2007). We argue that the relative accuracy of navigation in the horizontal and vertical dimensions makes sense in terms of normal ecological imperatives, and that brain plasticity can be recruited to facilitate robust bicoded processing if required.
Studies on honeybees suggest that visual processing of optic flow is dominated by information impinging on the ventral visual field (Dacke & Srinivasan Reference Dacke and Srinivasan2007), which makes ecological sense for an animal that predominantly flies in the horizontal plane when foraging for nutrition. In contrast, the stingless bee operates in dense tropical environments where flower resources are typically scattered horizontally and throughout a range of vertical heights of up to 40 metres in the forest canopy. These stingless bees have been shown to be equally proficient at gauging distance in both the horizontal and vertical planes, potentially using optic flow mechanisms in both ventral and lateral visual fields (Eckles et al. Reference Eckles, Roubik and Nieh2012). Nonetheless, honeybees do sometimes also have to operate in complex three-dimensional environments such as tropical forests. How might they deal with the complexity of reliable orientation in the vertical plane? We suggest below that honeybees are able to use information other than optic flow, and that their brains can learn to combine different visual perceptions to solve novel problems, in a manner consistent with the bicoded hypothesis.
Whilst honeybees do communicate horizontal direction and distance to hive mates through a symbolic dance communication language, this does not reliably communicate elevation (Dacke & Srinivasan Reference Dacke and Srinivasan2007). It is therefore likely that individual foragers must learn through their own experience to determine vertical components of their three-dimensional world. One possible solution to this problem is relationship learning – estimating vertical position by understanding the relative relationships, such as above/below, between different elemental features in the environment. The capacity to process such relationship rules is not innate for a brain. Three-months-old human babies do not show evidence of relationship processing, although by 6 months of age this capacity has developed (Quinn et al. Reference Quinn, Polly, Furer, Dobson and Narter2002). Other adult primates, such as capuchin monkeys (Cebus apella), also show a capacity for solving problems requiring the learning of above/below rules (Spinozzi et al. Reference Spinozzi, Lubrano and Truppa2004). Recent work in honeybees shows that while their brains do not innately code spatial relationship rules, individual free-flying bees can learn such relationships through visual experience, including the reliable processing of above/below (Avarguès-Weber et al. Reference Avarguès-Weber, Dyer, Combe and Giurfa2012).
The relationship rule processing mechanism observed in honeybees would thus give the potential for experienced individuals to forage in complex environments with acquired knowledge about relative vertical positions between biologically plausible objects, such as flowers and tree limbs (Chittka & Jensen Reference Chittka and Jensen2011; Dyer et al. Reference Dyer, Rosa and Reser2008). Could “vertical knowledge” then be combined with the perception of optic flow in the horizontal plane, to give a true bicoded perception of three-dimensional space? We believe so. The work on how honeybees process complex visual relationship rules, including above/below and same/different, suggests that there is also a capacity to learn simultaneously two separate rules or types of visual information, and then combine this acquired knowledge to solve novel problems (Avarguès-Weber et al. Reference Avarguès-Weber, Dyer, Combe and Giurfa2012). Thus, although the honeybee appears to process horizontal and vertical optic flows as separate signals (Dacke & Srinivasan Reference Dacke and Srinivasan2007), it does appear that their brains have the capacity to combine multiple sources of sensory perception and other spatial cues to make novel decisions in complex environments.
In summary, learning to build concepts to process multiple dimensions of three-dimensional navigation using a bicoded system as hypothesised by Jeffery et al. may represent a more general biological capacity, which likely extends to relatively simple brains such as those of insects. Further, we suggest that the opportunity for a brain of an individual to learn complex tasks through experience is critical to revealing the true behavioural capabilities in animals, irrespective of the relative number of neurons and synapses involved.