Experimental bias in number-line tasks and how to avoid them: Comment on Kim and Opfer (2017) and the introduction of the Cohen Ray number-line task.

Kim and Opfer (2017) report data that demonstrate children produce a negatively accelerating (e.g., logarithmic) response pattern in the unbounded number-line task. This pattern of results is the opposite of those generally reported for the unbounded number-line task (e.g., Cohen & Blanc-Goldhammer, 2011; Cohen & Sarnecka, 2014). We believe Kim and Opfer's (2017) experimental procedure inadvertently biased participants' data in the unbounded task. Here, we (a) outline the factors that induce experimental bias in computerized number-line tasks, (b) identify the likely source of experimental bias in Kim and Opfer (2017) that led to the negatively accelerating pattern of data, (c) introduce a new number-line variation (the universal number-line task), and (d) introduce a publicly available, open source number-line task that provides researchers with a simple, robust, and correct method for collecting data on the unbounded, bounded, and universal number-line tasks. We conclude that Kim and Opfer's (2017) implementation of the unbounded number-line is biased, and therefore cannot provide meaningful support for the log-to-linear shift hypothesis. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Construction and characterization of metal ion-containing DNA nanowires for synthetic biology and nanotechnology.

DNA is an attractive candidate for integration into nanoelectronics as a biological nanowire due to its linear geometry, definable base sequence, easy, inexpensive and non-toxic replication and self-assembling properties. Recently we discovered that by intercalating Ag+ in polycytosine-mismatch oligonucleotides, the resulting C-Ag+-C duplexes are able to conduct charge efficiently. To map the functionality and biostability of this system, we built and characterized internally-functionalized DNA nanowires through non-canonical, Ag+-mediated base pairing in duplexes containing cytosine-cytosine mismatches. We assessed the thermal and chemical stability of ion-coordinated duplexes in aqueous solutions and conclude that the C-Ag+-C bond forms DNA duplexes with replicable geometry, predictable thermodynamics, and tunable length. We demonstrated continuous ion chain formation in oligonucleotides of 11-50 nucleotides (nt), and enzyme ligation of mixed strands up to six times that length. This construction is feasible without detectable silver nanocluster contaminants. Functional gene parts for the synthesis of DNA- and RNA-based, C-Ag+-C duplexes in a cell-free system have been constructed in an Escherichia coli expression plasmid and added to the open-source BioBrick Registry, paving the way to realizing the promise of inexpensive industrial production. With appropriate design constraints, this conductive variant of DNA demonstrates promise for use in synthetic biological constructs as a dynamic nucleic acid component and contributes molecular electronic functionality to DNA that is not already found in nature. We propose a viable route to fabricating stable DNA nanowires in cell-free and synthetic biological systems for the production of self-assembling nanoelectronic architectures.