Our Gemara on Amud Aleph discusses more about Toch Kedei Dibur, that is a parcel of time that it takes to state, “Peace onto you, my master and teacher.” As we learned in Psychology of the Daf Nedarim 69, there are many halakhic distinctions that arise from this measure of time, mostly having to do with being allowed to renege or retract statements, conditions and agreements within this small time frame. Many commentaries understand this time frame to be based on either a rabbinic enactment, or a de facto assumption that a person does not fully finish their thought or resolve until he has a moment to consider and finalize it.
One of the challenges to that formulation is how our Gemara uses this measure of time. Our Gemara studies a scenario where a person performed the Keriyah ritual upon hearing that a specific relative died, and then he finds out it was a different relative. If the news reached him within a kedei dibbur of the rending of his clothes, the ritual is still valid and no further rending is obligatory.
The obvious question is, factually, he did Keriyah over an entirely different person! There is yeshivishe reyd that resolves this problem by explaining that Kedei Dibbur is not just a conditional situation, but actually a halakhic quanta of time. That is, time itself is measured in moments, and the halakhically reducible moment is toch kedei dibbur. Thus, the action and thought are still considered as simultaneous within this time zone, even though technically it is not.
(See ר שמעון שער יושר שער ה:כב, אחיעזר ב:כה;ז, דברי יחזקאל סימן כז ). As an example, one might measure time, in seconds or milliseconds, whatever that standard is. Therefore the Olympic judges will consider two runners that are tied to the measurable 100th of a second as simultaneous, even though we might argue that one runner was a millionth of a second faster.
Since this is Psychology of the Daf, I will offer a psycho-lomdishe answer to this question: A mourner is in some ways forbidden to talk, His mode of expression must be measured and sober. Rabbennu Bechaye (Vayikra 10:3) notes Aharon’s silence in the face of his sons’ sudden death. It is appropriate for the mourner to be silent and engage in introspection. Bava Basra (16b) tells us that mourners eat lentils, because it is a type of bean with no “mouth”; the bean has no obvious seam or opening. This alludes to the muted nature of the mourner.
Yet the mourner must express himself. The violent rending of his clothes is the quiet scream, like the wailing of the Shofar, a simulacrum of human anguish and cries If Keriyah is, in essence, a diverted and sublimated form of the mourner’s cry of anguish, then it is a substitute for speech. But more than a substitute, it is actually speech itself. Therefore, the Keriyah ritual is subject to the same terms and conditions of other forms of speech.
This posting is dedicated to those who can only scream silently, and may God hear and answer their cries.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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