Effects of phenosafranine (Ps) on the delayed formation of latent image specks in a vacuum and on the dispersion of latent image specks at sulfur-sensitized octahedral grain emulsions were studied by the arrested development technique. Ps desensitized in room air especially at unsensitized emulsion, while it was not the case in a vacuum. Ps did not affect the dispersion of latent image specks in room air and in a vacuum as well, while high level of sulfur sensitization enhanced the dispersion. Low levels of Ps and sulfur sensitization depressed the delayed formation, and high levels of both enhanced it. The sulfur sensitization may enhance the delayed formation due to the dispersion of latent image specks, while Ps may do so due to the formation of single silver atom species (SSAS). An emulsion grain is divided into several domains and the delayed formation proceeds when a latent sub-image speck and SSAS form in the same domain. There are two types of small silver species; growing species and nongrowing. The former is a precursor of the latent image speck acting as an electron trap. The later, such as SSAS, cannot trap electrons and it requires a certain aggregation process to grow a larger speck.