user-1: I have a fairly straightforward question. When I visualize without aim, or even sometimes with aim, disturbing or aggressive images sometimes arise in consciousness. Can I practice meditations on the brahma viharas without visualizing? 

user11009: To practice Brahma Viharas you should have at least one living being. 
So it is not possible to practice without an object.

user295: The subject of your meditation should be a subject which is a live being or some category or grouping of real living beings (loved ones, same part of the country, humans, some animals, northerners, neighbours,  etc.). You can use any visualization or verbalisations. But when you try to visualise X some other unrelated things happens. In this case do not react with despair and anger. When things are not in your control know that it is not / non self.
Also objective of Brahma Vihara is to:

develop these qualities
break the tendency to classify into favorable, unfavorable and neutral categories and  react to the sensations and feelings due to the perception creating unwholesome roots
break the tendency to classify into superior, inferior and neutral and and to react to them creating sensations and feelings due to the perception creating unwholesome roots


user8238: There is a Zen story that goes something like this, a Zen student ask the master if in the state of no thoughts, are there any sins left. The Master replied: "Sumeru!". Sumeru being the mythical World Mountain at the center of the world, a metaphor for immense afflictions.
The fact is that we have a great deal of suffering buried deep within our mind. And it is during the calm state of meditation that many start to surface. I once watched a documentary "Dhamma Brothers" about these prisoners who underwent an intensive 10 days meditation retreat. One of the things that stood out was that some of these murderers interviewed said they start to relive and become aware their horrible crimes. For them it was like coming out of a haze, and making realizations that they have hurt their victims unjustly.
This is why it is Ethics that is the foundation for a successful meditation practice, because we will be reliving a lot of our karma and negative mental habits. According to traditional Buddhist views, this buried afflictions are so deeply embedded all the way from our past lives.
So the question is what to do when these memories/thoughts/visual imaginations resurface? We should apply the antidote to these poisons in our mind. If we have deep anger and resentment for a person, we need apply compassion and forgiveness towards that person. The feelings of loving kindness and good will are the tool needed to overcome these negative mental states. ("Love" very much in the Christian sense). Repentance likewise is very helpful.

user-1: The practice of the brahma vihara meditation is given in the suttas as follows:

[One] dwells pervading one quarter with a mind imbued with [brahma-vihara quality], likewise the second quarter, the third quarter, and the fourth quarter. Thus above, below, across, and everywhere, and to all as to himself, he dwells pervading the entire world with a mind imbued with [brahma-vihara quality], vast, exalted, measureless, without enmity, without ill will.

Where the quality in brackets stands for one of the four immeasurables: mettā, karuṇā, muditā, upekkhā ("loving-kindness", "compassion", "empathetic joy", "equanimity").
If we regard this practice description as complete, we can follow it as is. In this case, it doesn't seem to emphasize specific visualizations. Instead, it seems to instruct us to do an active immersion of the mind in a certain quality, say, spreading it and filling every corner of one's mind with it.
Using mettā as example, one immerses the mind in this quality gradually:

[...] one quarter with a mind imbued with mettā, likewise the second quarter, the third quarter, and the fourth quarter [...]

One makes it pervasive, ubiquitous:

Thus above, below, across, and everywhere [...] vast, exalted, measureless

One directs it and applies it to every being, to the entire world:

[...] to all as to himself, he dwells pervading the entire world with a mind imbued with mettā.

When this practice is undertaken, unwholesome qualities diminish:

[...] without enmity, without ill will.

They diminish because if these are effectively practiced, the mind becomes interested in these qualities; it grabs the interest of the mind once it finds them pleasurable. As result, the mind incorporates them.
They also diminish because of "incompatibility". For example, it's not possible for a mind immersed in compassion to have cruelty taking hold of it. Cruel thoughts appear distant, tasteless, sterile and weak in a mind soaked in compassion.

With the brief practice contextualized, let's talk the specifics:
You said: disturbing or aggressive images sometimes arise in consciousness.
If the aggressive images that arise (e.g. towards another or towards oneself) are born out of anger or are enticing, metta and/or karuna can be ideal primary practices. If the aggressive images are born out of envy,  jealous or discontent sentiments, it might be interesting to focus more on mudita (see AN 6.13 and also DN 34). All these can be complemented and calibrated by upekkhā, which is also one of the recommended practices for dealing with disgust and passion.
On the other hand, if the disturbing thoughts have as origin remorse or, generally, non-virtuous past behaviors, it might be fruitful to focus more on reestablishing the precepts, making amends to past mistakes and strengthening virtuous behavior.
Naturally, all the above are not mutually exclusive, meaning one benefits from doing them all, but certain difficulties might be approached better with a focused/dedicated effort.

user-1: Those are perfect appearances, Eggman. Developing, for example metta means to hold on an attitude of goodwill (metta) "like a mother holds on here only son", even so hold on a mindstate of metta. Special perfect, because those phenomenas cause you to fall into aversion. That's a perfect working place. So when such things arise, put more effort into keeping up goodwill and don't tend to aversion if it arises. Itks good when you also observe how mind reacts, phenomenas arising and decay. When you use metta as object for your concentration (thats actually the dhammic purpose of it), also obsere the comming and going of phenomenas. It's good to become aware of such, much better then to dwell dull in the Brahma Vihara realm.

-1: <p>I have a fairly straightforward question. When I visualize without aim, or even sometimes with aim, disturbing or aggressive images sometimes arise in consciousness. Can I practice meditations on the brahma viharas without visualizing? </p>
 11009: <p>To practice Brahma Viharas you should have at least one living being. </p>

<p>So it is not possible to practice without an object.</p>
 295: <p>The subject of your meditation should be a subject which is a live being or some category or grouping of real living beings (loved ones, same part of the country, humans, some animals, northerners, neighbours,  etc.). You can use any visualization or verbalisations. But when you try to visualise X some other unrelated things happens. In this case do not react with despair and anger. When things are not in your control know that it is not / non self.</p>

<p>Also objective of Brahma Vihara is to:</p>

<ul>
<li>develop these qualities</li>
<li>break the tendency to classify into favorable, unfavorable and neutral categories and  react to the sensations and feelings due to the perception creating unwholesome roots</li>
<li>break the tendency to classify into superior, inferior and neutral and and to react to them creating sensations and feelings due to the perception creating unwholesome roots</li>
</ul>
 8238: <p>There is a Zen story that goes something like this, a Zen student ask the master if in the state of no thoughts, are there any sins left. The Master replied: "Sumeru!". Sumeru being the mythical World Mountain at the center of the world, a metaphor for immense afflictions.</p>

<p>The fact is that we have a great deal of suffering buried deep within our mind. And it is during the calm state of meditation that many start to surface. I once watched a documentary "Dhamma Brothers" about these prisoners who underwent an intensive 10 days meditation retreat. One of the things that stood out was that some of these murderers interviewed said they start to relive and become aware their horrible crimes. For them it was like coming out of a haze, and making realizations that they have hurt their victims unjustly.</p>

<p>This is why it is Ethics that is the foundation for a successful meditation practice, because we will be reliving a lot of our karma and negative mental habits. According to traditional Buddhist views, this buried afflictions are so deeply embedded all the way from our past lives.</p>

<p>So the question is what to do when these memories/thoughts/visual imaginations resurface? We should apply the antidote to these poisons in our mind. If we have deep anger and resentment for a person, we need apply compassion and forgiveness towards that person. The feelings of loving kindness and good will are the tool needed to overcome these negative mental states. ("Love" very much in the Christian sense). Repentance likewise is very helpful.</p>
 -1: <p>The practice of the brahma vihara meditation is given in the suttas as follows:</p>

<blockquote>
  <p>[One] dwells pervading one quarter with a mind imbued with <strong>[brahma-vihara quality]</strong>, likewise the second quarter, the third quarter, and the fourth quarter. Thus above, below, across, and everywhere, and to all as to himself, he dwells pervading the entire world with a mind imbued with <strong>[brahma-vihara quality]</strong>, vast, exalted, measureless, without enmity, without ill will.</p>
</blockquote>

<p>Where the quality in brackets stands for one of the four immeasurables: <em>mettā, karuṇā, muditā, upekkhā</em> ("loving-kindness", "compassion", "empathetic joy", "equanimity").</p>

<p>If we regard this practice description as complete, we can follow it as is. In this case, it doesn't seem to emphasize specific visualizations. Instead, it seems to instruct us to do an active immersion of the mind in a certain quality, say, spreading it and filling every corner of one's mind with it.</p>

<p>Using mettā as example, one immerses the mind in this quality gradually:</p>

<blockquote>
  <p>[...] one quarter with a mind imbued with mettā, likewise the second quarter, the third quarter, and the fourth quarter [...]</p>
</blockquote>

<p>One makes it pervasive, ubiquitous:</p>

<blockquote>
  <p>Thus above, below, across, and everywhere [...] vast, exalted, measureless</p>
</blockquote>

<p>One directs it and applies it to every being, to the entire world:</p>

<blockquote>
  <p>[...] to all as to himself, he dwells pervading the entire world with a mind imbued with mettā.</p>
</blockquote>

<p>When this practice is undertaken, unwholesome qualities diminish:</p>

<blockquote>
  <p>[...] without enmity, without ill will.</p>
</blockquote>

<p>They diminish because if these are effectively practiced, the mind becomes interested in these qualities; it grabs the interest of the mind once it finds them pleasurable. As result, the mind <em>incorporates</em> them.</p>

<p>They also diminish because of "incompatibility". For example, it's not possible for a mind immersed in compassion to have cruelty taking hold of it. Cruel thoughts appear distant, tasteless, sterile and weak in a mind soaked in compassion.</p>

<hr>

<p>With the brief practice contextualized, let's talk the specifics:</p>

<p>You said: <code>disturbing or aggressive images sometimes arise in consciousness.</code></p>

<p>If the aggressive images that arise (e.g. towards another or towards oneself) are born out of anger or are enticing, <em>metta</em> and/or <em>karuna</em> can be ideal primary practices. If the aggressive images are born out of envy,  jealous or discontent sentiments, it might be interesting to focus more on <em>mudita</em> (see <a href="https://suttacentral.net/en/an6.13" rel="nofollow noreferrer">AN 6.13</a> and also <a href="https://suttacentral.net/en/dn34" rel="nofollow noreferrer">DN 34</a>). All these can be complemented and calibrated by <em>upekkhā</em>, which is also one of the recommended practices for dealing with disgust and passion.</p>

<p>On the other hand, if the disturbing thoughts have as origin remorse or, generally, non-virtuous past behaviors, it might be fruitful to focus more on reestablishing the precepts, making amends to past mistakes and strengthening virtuous behavior.</p>

<p>Naturally, all the above are not mutually exclusive, meaning one benefits from doing them all, but certain difficulties might be approached better with a focused/dedicated effort.</p>
 -1: <p>Those are perfect appearances, Eggman. Developing, for example metta means to hold on an attitude of goodwill (metta) "like a mother holds on here only son", even so hold on a mindstate of metta. Special perfect, because those phenomenas cause you to fall into aversion. That's a perfect working place. So when such things arise, put more effort into keeping up goodwill and don't tend to aversion if it arises. Itks good when you also observe how mind reacts, phenomenas arising and decay. When you use metta as object for your concentration (thats actually the dhammic purpose of it), also obsere the comming and going of phenomenas. It's good to become aware of such, much better then to dwell dull in the Brahma Vihara realm.</p>
