A 50 min time series of one-dimensional slit-spectrograms, taken in quiet sun at disk centre, observed at the German Vacuum Tower Telescope (Observatorio del Teide), was used to study the global and spatial variations of different line parameters. In order to determine the vertical structure of the photosphere two lines with well separated formation heights have been considered. The data have been filtered of p-modes to isolate the pure convective phenomenon. From our studies of global correlation coefficients and coherence and phase shift analyses between the several line parameters, the following results can be reported. The convective velocity pattern preserves structures larger than 1.0 arcs to the highest layers of the photosphere ( ~ 435 km). However, at these layers, in the intensity pattern only structures larger than 2.0 arcs are still connected with those at the continuum level although showing inverted brightness contrast. This confirms an inversion of temperature that we have found at a height of ~ 140 km. A possible evidence of gravity waves superimposed to the convective motions is derived from the phase shift analysis. We interprete the behaviour of the full width at half maximum and the equivalent width as a function of the distance to the granular borders, as a consequence of enhanced turbulence and/or strong velocity gradients in the intergranular lanes.