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10. Hedges, S.B., Blair, J.E., Venturi, M.L., and relations between Gromia and Foraminifera. in the shadow of giant protists. Paleont. Res. 7, Shoe, J.L. (2004). A molecular timescale of Acta Protozool. 43, 303–311. 43–54. eukaryote evolution and the rise of complex 15. Pawlowski, J., Holzmann, M., Berney, C., 20. Peterson, K.J., Cotton, J.A., Gehling, J.G., and multicellular life. BMC Evol. Biol. 4, 2. Fahrni, J., Gooday, A.J., Cedhagen, T., Pisani, D. (2008). The Ediacaran emergence of 11. Douzery, E.J.P., Snell, E.A., Bapteste, E., Habura, A., and Bowser, S.S. (2003). The bilaterians: congruence between the genetic Delsuc, F., and Philippe, H. (2004). The timing of evolution of early Foraminifera. Proc. Natl. and the geological fossil records. Phil. Trans. eukaryotic evolution: does a relaxed molecular Acad. Sci. USA 100, 11494–11498. R. Soc. Lond. B. 363, 1435–1443. clock reconcile proteins and fossils? Proc. Natl. 16. Gooday, A.J. (2002). Organic-walled Acad. Sci. USA 101, 15386–15391. allogromiids: aspects of their occurrence, 1 12. Hedley, R.H. (1962). Gromia oviformis diversity and ecology in marine habitats. Department of Zoology and Animal (Rhizopodea) from New Zealand with J. Foramin. Res. 32, 384–399. Biology, University of Geneva, Sciences III, comments on the fossil Chitinozoa: 17. Wilding, T.A. (2002). Taxonomy and ecology of 1211 Geneva 4, Switzerland. 2National New Zealand. J. Sci. 5, 121–136. Toxisarcon alba, sp. nov. from Loch Linnhe, Oceanography Centre, Southampton, Ocean 13. Nikolaev, S.I., Berney, C., Fahrni, J., Bolivar, I., west coast of Scotland, UK. J. Foramin. Res. Biogeochemistry and Ecosystems, European Polet, S., Mylnikov, A.P., Aleshin, V.V., 32, 358–363. Petrov, N.B., and Pawlowski, J. (2004). The 18. Gooday, A.J., Bowser, S.S., Bett, B.J., and Way, Southampton SO14 3ZH, UK. twilight of Heliozoa and rise of Rhizaria: an Smith, C.R. (2000). A large testate protist, E-mail: [email protected]; ang@noc. emerging supergroup of amoeboid eukaryotes. Gromia sphaerica sp. nov. (Order Filosea), from soton.ac.uk Proc. Natl. Acad. Sci. USA 101, 8066–8071. the bathyal Arabian Sea. Deep-Sea Res. II 47, 14. Longet, D., Burki, F., Flakowski, J., Berney, C., 55–73. Polet, S., Fahrni, J., and Pawlowski, J. (2004). 19. Seilacher, A., Grazhdankin, D., and Legouta, A. Multigene evidence for close evolutionary (2003). Ediacaran biota: the dawn of animal life DOI: 10.1016/j.cub.2008.11.003

Visual Perception: Tracking the In their monkey study, Wilke et al. [3] recorded target-evoked multi-unit Elusive Footprints of Awareness activity and local-field potentials in visual areas V1, V2, and V4. They found that fluctuations in the perceptual Subjective visual experience leaves two distinct, overlapping ‘footprints’ within presence of the target was reflected visual cortex: a small ‘footprint’ evident in multi-unit activity, and a much larger only in the multi-unit activity of area V4; ‘footprint’ that dominates activity indexed by haemodynamic responses. in areas V1 and V2, neither multi-unit activity nor high frequency local-field Randolph Blake1 and Jochen Braun2 target surrounded by moving dots with potentials reflected the perceptual responses associated with physical state reported by the monkey. At a professional meeting in 1999 an removal of that target. In two of these Interestingly, however, the lower overwhelmingly popular presentation studies, the ones by Wilke et al. [3] and frequency bands of the local-field was a poster manned by Yoram Maier et al. [4], macaque monkeys were potential presented a completely Bonneh from Israel’s Weizmann trained to report their perceptual different picture: here, the power of Institute. Throngs of people crowded experiences while viewing a highly the target response, which was around his video monitor to experience visible target presented to one eye reduced by the onset of the moving what can only be characterized as together with a field of moving dots dots, was reduced in all three areas (V1, visual magic: a small cluster of presented to the other eye or to both V2 and V4), more so when the target stationary yellow dots disappeared eyes; the moving dots surrounded but disappeared from perception than from visual awareness for seconds did not occlude the target. In the large when it remained visible. The latency of at a time when those dots were majority of these trials, the animal these perception-related reductions in surrounded by a swarm of coherently reported that the target, although the low frequency local-field potential moving blue dots [1]. You can physically present, disappeared components increased from V1 to V2 to experience a version of this compelling perceptually. Results from interleaved V4, suggesting a feed-forward signal. phenomenon by navigating to: http:// control trials on which the target A tantalizing parallel to these results www.michaelbach.de/ot/mot_mib/ remained visible or on which it emerges in the recent study by Donner Dubbed ‘motion-induced blindness’, disappeared physically confirmed the et al. [5], who used functional magnetic this beguiling visual illusion strikingly reliability and accuracy of the animal’s resonance imaging (fMRI) to measure dissociates perception from reality reports. In the third study, by Donner blood oxygen level dependent (BOLD) and, thus, provides a powerful tool for et al. [5], human observers viewed signals in multiple visual cortical areas identifying the neural concomitants of a clearly visible target while a cloud of in the human brain. Evaluating the consciousness [2]. Three recent dots rotated around (but never over) BOLD activity that accompanies studies [3–5], employing closely related the target, thus causing the target perceptual target disappearance and motion-induced blindness paradigms intermittently to disappear from reappearance during motion induced in monkeys and in humans, have now perception for several seconds at blindness, the authors focused on the put this tool to excellent use to a time. Donner et al. [5] also included retinotopic representation of the target unearth results that appear neatly a replay condition in which the target in ventral visual areas V1, V2, V3 and V4. complementary and, for the most was physically turned on and off in After discounting contaminations to part, consistent. a temporal sequence mimicking the the target response by attention (which All three studies contrasted neural target’s perceptual fluctuations from is likely drawn to a perceptual transient) responses associated with perceptual a previous motion induced blindness and by non-specific modulations (see disappearance of a readily visible trial. below), the authors found that only Dispatch R31

within V4 did BOLD activity track the A perceptual state of the target, dipping at or around the time the target perceptually disappeared and rising Percept again when the target perceptually reappeared. The absence of perception-related BOLD modulations in areas V1, V2 and V3 stands in stark contrast to the significant BOLD modulations in these areas on the Stimulus replay trials when the target was physically turned on and off. In addition to this retinotopically localized modulation in BOLD Time responses, Donner et al. [5] also uncovered a second correlate of B perceptual target disappearance, this one seen throughout the entire representation of the visual field including the target area, the area covered by moving dots, and the visual periphery. This ‘global’ response was delayed with respect to perceptual disappearance and was also present when the target was physically removed. Perhaps the global modulation accompanying target disappearance, whether physical or V1 perceptual, is related to the surprisingly widespread activation that accompanies perceptual decisions in V4 early visual areas [6]. So taken together, the studies by Wilke et al. [3] and Donner et al. [5] Target subregion suggest that fluctuations of perceptual experience in the context of motion- induced blindness leave not one, but two overlapping ‘footprints’ in the activity of visual cortex: a small and Current Biology retinotopically specific ‘footprint’ in higher visual areas, notably area V4, Figure 1. Neural footprints of motion-induced blindness. and a larger and retinotopically (A) In motion-induced blindness, a clearly visible target (yellow arc) intermittently disappears nonspecific ‘footprint’ at all levels of from visual awareness when surrounded by a swarm of moving dots. (B) Two distinct, overlapp- the visual hierarchy, beginning in area ing ‘footprints’ of this perceptual disappearance have now been identified in visual cortex. A V1 (Figure 1). Interestingly, the small ‘footprint’ is readily evident in multi-unit recordings (spike rate and high-frequency local-field potential) in the target subregion of visual area V4 (intense yellow) [3]. A large ‘foot- salience of these two ‘footprints’ print’, covering the entire visual field representation in visual areas V1, V2, V3 and V4 (pale depends on the method used to assay yellow), modulates the haemodynamic response [5]. A more refined analysis resolves this cortical activity: the large footprint is seeming inconsistency: a small ‘footprint’, which is restricted to area V4, is discernable also barely noticeable in multi-unit in the haemodynamic response. Similarly, multi-unit recordings show a subtle modulation of recordings — its only trace being in the low-frequency local-field-potential also in areas V1 and V2, at least within the retinotopic the low-frequency local-field target representation [3,4]. It is still unclear whether this modulation also extends to other parts of the visual field, as does the large ‘footprint’ in the haemodynamic response. (We thank potential — but becomes readily Tobias Donner for preparing the figure.) evident in BOLD activity. Conversely, the small footprint is very evident in multi-unit recordings (both in multi-unit The differential salience of the two response tracked perceptual activity and in high-frequency- neural concomitants of motion- disappearance, whereas the spiking local-field potential), but is barely induced blindness also shows up in activity did not. Physical removal of discernable in BOLD activity. In fact, work of Maier et al. [4], who compared the target, however, was evident in only an exceptionally well-controlled single-unit recordings and BOLD both BOLD and spiking responses. experimental paradigm, such as that by activity measured in awake monkeys The only neurophysiological Donner et al. [5], could hope to reliably experiencing motion-induced correlate of this large BOLD identify the small footprint, as it is blindness. Focusing on the retinotopic modulation in V1 was a subtle virtually swamped by the large footprint representation of the target in visual reduction in low-frequency local-field in the BOLD response. area V1, they found that the BOLD potential power. Current Biology Vol 19 No 1 R32

But one question remains It would be gratifying if the same References 1. Bonneh, Y., Cooperman, A., and Sagi, D. (2001). unanswered: is there correspondence convergence could be realized in the Motion induced blindness in normal observers. between the motion-induced case of binocular rivalry, another Nature 411, 798–801. blindness-related BOLD modulations compelling phenomenon in which 2. Kim, C.Y., and Blake, R. (2005). Psychophysical magic: rendering the visible ‘‘invisible’’. Trends observed in human and in monkey visual awareness fluctuates even Cogn. Sci. 9, 381–388. area V1? Donner et al. [5] observed though physical stimulation remains 3. Wilke, M., Logothetis, N.K., and Leopold, D.A. (2006). Local field potential reflects a global but no target-specific invariant [2]. In the rivalry literature, perceptual suppression in monkey visual modulation (that is, activation stronger there are nagging inconsistencies cortex. Proc. Natl. Acad. Sci. USA 103, in target than in non-target voxels) between human brain imaging results 17507–17512. 4. Maier, A., Wilke, M., Aura, C., Zhu, C., Ye, F.Q., in human V1, whereas Maier et al. [4], and monkey single-cell results, but no and Leopold, D.A. (2008). Divergence of fMRI who did not compare target with one has yet recorded single-unit and neural signals in V1 during perceptual suppression in the awake monkey. Nat. non-target voxels, could not draw activity, BOLD signals and local-field Neurosci. 11, 1193–1199. this distinction. Perhaps, then, the potentials during rivalry. Brain imaging 5. Donner, T.H., Sagi, D., Bonneh, Y.S., and motion induced blindness-related studies of humans experiencing Heeger, D.J. (2008). Opposite neural signatures of motion-induced blindness in human dorsal BOLD modulations in monkey V1 binocular rivalry reveal widespread, and ventral visual cortex. J. Neurosci. 28, are global in nature and, therefore, perception-related modulations of 10298–10310. 6. Jack, A.I., Shulman, G.L., Snyder, A.Z., present within retinotopic regions BOLD responses, including within the McAvoy, M., and Corbetta, M. (2006). Separate of V1 well beyond the target lateral geniculate nucleus, V1 and modulations of human V1 associated with representation. higher visual areas [9]. This distribution spatial attention and task structure. Neuron 51, 135–147. So, thanks to the potent, intermittent of brain regions differs from those 7. Scholvinck, M., and Rees, G. (2008). Neural perceptual suppression of vision exhibiting target-related BOLD correlates of motion-induced blindness in the human brain [Abstract]. J. Vis. 8, 793a. induced by motion induced blindness, modulations during motion-induced http://journalofvision.org/8/6/793/. we are beginning to see how different blindness, implying that the two DOI: 10.1167/8.6.793. components of neural responses phenomena are not mediated by the 8. Libedinsky, C., Savage, T., and Livingstone, M. (2008). Nature Precedings: within the visual hierarchy are related same neural circuits. However, the hdl:10101/npre.2008.1506.1. to fluctuations in visual perception, distinct circuits producing these two 9. Tong, F., Meng, M., and Blake, R. (2006). Neural bases of binocular rivalry. Trends Cogn. and we can expect to learn even phenomena may embody equivalent Sci. 10, 502–511. more about the neural concomitants neural operations that lead to equally of motion induced blindness in the compelling fluctuations in visual 1512 Wilson Hall, Vanderbilt University, near future [7,8]. Moreover, we are perception, in which case we could Nashville, TN 37240, USA. 2Institute of beginning to witness some reasonably hope to see the same Biology, Otto-von-Guericke University, convergence between the results of neural footprints associated with 39120 Magdeburg, Germany. monkey neurophysiology and human spiking, BOLD and local-field E-mail: [email protected]; brain imaging in situations where potentials for rivalry and motion [email protected] perception and physical stimulation induced blindness, albeit in different are dissociated. brain areas. DOI: 10.1016/j.cub.2008.11.009

Evolutionary Cooperation: Male the Prisoner’s dilemma [3] or the tragedy of the commons [4], whereby Cleaner Fish Aggression May individuals do best by not cooperating (cheating), no matter what their Promote Female Cooperation partners do. This results in an inevitable outcome (hence ‘tragic’) in which all rational actors cheat, even though they A new study has shown that mixed-sex pairs of cleaner fish provide a better — all would be better off in the long-term if more cooperative — service than singletons despite pairs facing an apparent they had all cooperated, hence the Prisoner’s dilemma. dilemma [3,4]. A new study by Bshary et al. [5] has Maxwell N. Burton-Chellew theory of inclusive fitness [1,2], which now shown that cooperation is explains how seemingly achieved between individuals of Why would Darwinian evolution disadvantageous alleles can also a cleaner reef-fish species (Labroides produce organisms that act to increase their transmission indirectly dimidiatus) that service shared clients increase the success of others? The by helping other individuals, typically (Figure 1), primarily because females evolution of such behaviour is close relatives, that are likely to share are more cooperative towards their problematic because, at first sight, the same allele [1,2]. Yet cooperation clients when they are working with cooperative behaviours appear to be also occurs between unrelated a male than when alone. This disadvantageous, and yet cooperation individuals and even between different facultative cooperation may be is witnessed throughout Nature. The species. The inherent instability of such a response to the threat of male most powerful and successful cooperation between non-relatives aggression. The nature of this explanation has been Hamilton’s is often conceptualised with the aid of cooperation provides an added twist