Frequency dependence of the conductivity and dielectric constant of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">La</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CuO</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn><mml:mo>+</mml:mo><mml:mi mathvariant="normal">y</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>near the insulator-metal transition

Measurements are reported of the conductivity and dielectric constant at frequencies up to 10 MHz for a single crystal of ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4+\mathrm{y}}$ with y\ensuremath{\sim}0.001 to 0.01. The reported behavior is typical of conventional doped semiconductors, with dielectric constant (at y=0) and effective mass that are not exceptionally large. The dielectric constant grows as the insulator-to-metal transition is approached, but only for the electric field in the ${\mathrm{CuO}}_{2}$ layers, indicating that the transition is two dimensional. The crossover to weak localization occurs close to the antiferromagnetic phase boundary.