How did laryngeal consonants affect neighboring vowels in Proto-Indo-European?

In Proto-Indo-European (PIE), the existence of laryngeal consonants—most commonly reconstructed as $H_1$, $H_2$, and $H_3$—is primarily deduced from their transformative effects on neighboring vowels.12

These consonants influenced vowels in two primary ways:

• Vowel Quality: The laryngeals altered the color of adjacent vowels. Specifically, $H_2$ changed a neighboring $e$ to $a$, and $H_3$ likely changed a neighboring $e$ to $o$.12
• Vowel Length: All three laryngeals caused the lengthening of a preceding vowel within the same syllable.12

Additionally, when laryngeals occurred between consonants and subsequently disappeared, they often left behind a vocalic remnant. Before the development of the laryngeal theory, linguists accounted for these resulting vowels by reconstructing a separate PIE vowel known as the schwa indogermanicum ($\partial$). While these sounds largely vanished or merged in most Indo-European languages, the Anatolian branch, particularly Hittite, preserved them as $h$ or $hh$ in certain positions, providing critical evidence for their original existence.123