A crude plot of average hominid brain sizes over time.

<p>Although after an initial flatlining this plot appears to show consistent enlargement of hominid brains over the last 2 million years, it is essential to note that these brain volumes are averaged across a number of independent lineages within the genus <i>Homo</i> and likely represent the preferential success of larger-brained species. From <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001934#pbio.1001934-Tattersall1" target="_blank">[20]</a>. <i>Image credit: Gisselle Garcia, artist (brain images)</i>.</p

The binary operation of <i>merge</i> (X,Y) when Y is a subset of X leads to the ubiquitous phenomenon of “displacement” in human language, as in <i>Guess what boys eat</i>.

<p>Left: The circled structure Y, corresponding to <i>what</i>, the object of the verb <i>eat</i>, is a subset of the circled structure X, corresponding to <i>boys eat what</i>. Right: The free application of <i>merge</i> to X, Y in this case automatically leads to <i>what</i> occupying two syntactic positions, as required for proper semantic interpretation. The original <i>what</i> remains as the object of the verb so that it can serve as an argument to this predicate, and a copy of <i>what</i>, “displaced,” is now in the position of a quantificational operator so that the form can be interpreted as “for what <i>x</i>, boys eat <i>x</i>.” Typically, only the higher <i>what</i> is actually pronounced, as indicated by the line drawn through the lower <i>what</i>.</p

Correlation coefficients of the relationship between the number of elements copied from the tutor song and Zenk expression in the HVC, RA and Area X for groups of birds exposed to the tutor song (TUTOR), bird’s own song (BOS), or novel conspecific song (NOVEL).

a<p>NS, Not Significant; p-values <0.05 were considered significant.</p

Mean (± SEM) number of Zenk-positive nuclei per mm² in the song system brain nuclei (A) HVC, (B) RA and (C) Area X, for groups of male zebra finches exposed to tutor song (TUTOR), bird’s own song (BOS) or novel conspecific song (NOVEL).

<p>Mean (± SEM) number of Zenk-positive nuclei per mm² in the song system brain nuclei (A) HVC, (B) RA and (C) Area X, for groups of male zebra finches exposed to tutor song (TUTOR), bird’s own song (BOS) or novel conspecific song (NOVEL).</p

Scatter plots of mean number of Zenk immunoreactive cell nuclei per mm² in the song system nucleus HVC, in relation to the percentage of song elements copied from the tutor song (song similarity) for groups of birds exposed to (A) tutor song (TUTOR), (B) bird’s own song (BOS) or (C) novel conspecific song (NOVEL).

<p>Note that y-axis has a log scale.</p

Schematic diagrams of composite views of parasagittal sections of the songbird brain.

<p>A. Diagram of a songbird brain giving approximate positions of nuclei and brain regions involved in auditory perception and memory. Yellow areas represent brain regions that show increased neuronal activation when the bird hears song. B. Diagram of a songbird brain giving approximate positions of nuclei and brain regions involved in vocal production and sensorimotor learning. Orange nuclei in the song system show increased neuronal activation when the bird is singing. Abbreviations: CLM, caudal lateral mesopallium; CMM, caudal medial mesopallium; DLM, nucleus dorsolateralis anterior, pars medialis; HVC, acronym used as a proper name; L1, L2, L3, subdivisions of Field L; LMAN, lateral magnocellular nucleus of the anterior nidopallium; NCM, caudal medial nidopallium; nXIIts, tracheosyringeal portion of the nucleus hypoglossus; RA, robust nucleus of the arcopallium. Modified and reproduced, with permission, from references <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041556#pone.0041556-Bolhuis5" target="_blank">[9]</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041556#pone.0041556-Moorman2" target="_blank">[60]</a>, copyright 2010 Nature Publishing Group. All rights reserved.</p

Meaning depends on syntactic structure.

<p>In Fig 1A, the phrase consists of the verb <i>saw</i> and the object of the verb <i>the man with the binoculars</i>, itself consisting of the noun phrase the man and a modifying prepositional complement <i>with the binoculars</i>. First, the modifying complement and the noun phrase are combined in what will be the object of the verb. The phrase in Fig 1B consists of a verb (<i>saw</i>), the object of the verb (<i>the man</i>), and an adjunct (<i>with the binoculars</i>), the means by which the man is seen. First, the object is combined with verb, and then this result is combined with the adjunct.</p

String arrangements.

<p>In Fig 2A the phrase is interpreted as [[old men] and [women]], i.e., “a collection of women (young or old) and old men.” In contrast, in Fig 2B, the phrase is interpreted as [old [men and women]], i.e., “a collection of men and women, all of them old.” ADJ, adjective; N, noun; NP, noun phrase</p

Data acquisition.

<p>Schematical representation of the auditory stimulation design. The entire paradigm was repeated 6 times with alternate presentation of the six different stimuli BOS, reversed BOS, random BOS, familiar CON, BOS ripples, and WN.</p

Average BOLD signal of one example bird (see online edition for color figure).

<p>The images illustrate the typical activation pattern that was found in all experimental birds. The signal shown here is for all sounds presented and all brain images averaged together. The left panel shows the <i>P</i>-values of significant activated pixels, the right panel shows the signal strength relative to the mean signal difference. The three lines show the division in regions of interest conform <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003184#pone-0003184-g003" target="_blank">Figure 3</a>.</p